Sensitivity of drosophila mutants to chemical carcinogens.

7 single-mutant and five double-mutant strains of Drosophila melanogaster were tested for their relative sensitivity to the chemical carcinogens: 1-acetylaminofluorene, benzo(alpha)pyrene, N-methyl-N'-nitro-N-nitrosoguanidine, 4-nitro quinoline-1-oxide and aflatoxin B1. Among the single mutants, mei-9a, mei-41D5 and mus(1)104D1 are hypersensitive to all 5 chemicals, whereas mus(1)107D1 is hypersensitive only to 4-nitroquinoline-1-oxide and is slightly sensitive to benzo(alpha)pyrene. The mei-9a mei-41D5 double-mutant is the most sensitive of 5 tested double-mutants which carry the mei-9a allele. When treated with 0.025 mM benzo(alpha)pyrene this double-mutant produces significantly more sex-linked recessive lethals and dominant lethals than does the control. Analysis of double-mutants reveals that the mei-9+ product functions in a different repair pathway of methyl methanesulfonate-induced damage than do the normal products of the mus(1)103, mus(1)104 and mus(1)107 loci. Our findings suggest that the sensitivity of Drosophila repair-deficient mutants could be exploited in screening for potential mutagens and carcinogens.     

Occurrence of spontaneous and nitrosoethylurea-induced mutations and potential changes in repair-deficient Drosophila strains

X-linked recessive lethal frequencies in mature spermatozoa were studied in repair-deficient Drosophila strains. Frequencies of spontaneous and ethylnitrosourea-induced lethals were enhanced in mus(I)104DI+ and unchanged in mei-9IL+. In addition, the majority of lethals was fixed in stages preceding mature spermatozoa. It was shown that premutational lesions (spontaneous and ethylnitrosourea-induced in both mutants) arise in germ cells, these lesions being realized into mutations in the next generations.     

Genetic damage induced by X-rays or neutrons in spermatozoa of Drosophila melanogaster; differential processing in the oocytes of females carrying the DNA-repair-deficient mutants mei-9a and mus-101d1

Radiation-induced premutational lesions on the chromosomes of irradiated mature spertozoa of Drosphila are processed when the sperm nucleus the egg cytoplasm at fertilization. This processing depends on enzymatic repair systems, which are built up in ocytes under the control of the maternal genotype. The present study is concerned with 2 repair-deficient mutants, mei-9^a and mus-101^D1. Irradiated Basc males were crossed to homozygous mei-9^a or mus-101^D1 females, or to repair-proficient control females. The frequencies of recovered sex-link recessive lethal mutations and of II–III translocations were used to assess the effects of impaired maternal repair. Neutrons, as a densely ionizing radiation, and X-rays as a sparsely ionizing one, were used to induce the premutational lesions.The question being asked was whether different radiation qualities cause specific types of lesion that are processed differentially under conditions of impaired maternal repair. The results indicate that this may be so. In comparison with the control, with repair-proficient females, all major effects caused by impaired maternal repair led to frequency reductions in the recovery of lethals and translocations. These reductions in yield were pronounced in all neutron experiments, whereby mus-101^D1 had a stronger effect than mei-9^a. Two possible explanations are considered. The first is based on the idea that specific lesions are processed in a specific way, resulting in a specific mutational end-product, which may not be recovered when repair is impaired. The second is based on the notion that energy deposition in cells exposed to neutrons is not uniform, which leads to clustered damage. Impaired repair may select againts multiply damaged cells much more powerfully than normal repair. Consequently, the surviving fraction of cells is likely to have received less than the average dose. With X-rays, no or only spurious effects of the repair-defective mutants were detected, except in the following case: recovery of translocations (but not of lethals) was strongly reduced when irradiated males were crossed to mus-101^D1 females. It is assumed that mus-101^D1 is defective in repair of DNA double-strand damage, and that the formation of translocations may depend particularly on this repair function.     

Studies on mutagen-sensitive strains of Drosophila melanogaster. VII. Effects of repair deficiency in males on X-ray-induced sex-linked recessive lethals in spermatozoa

The response of mature spermatozoa to the X-ray induction (500 R and 3000 R) of sex-linked recessive lethals was studied in Drosophila melanogaster males known to be deficient in excision- or post-replication repair of UV damage in somatic cells. The results show that the induced frequencies of recessive lethals in the excision-repair-deficient males (mei-9a and mei-9L1) are similar to those in the appropriate repair-proficient males (mei+ and Berlin-K). However, in the post-replication-repair-deficient males (w mus(1)101D1), these frequencies are significantly lower than in the comparable repair-proficient males (w) after 500 R, but not after 3000 R.     

Studies on mutagen-sensitive strains of Drosophila melanogaster. IV. Modification of genetic damage induced by X-irradiation of spermatozoa and spermatids in N2 or O2 by mei-9a, mei-41D5 and mus(1)101D1

The influence of defects in DNA repair processes on X-ray-induced genetic damage in post-meiotic male germ cell stages of Drosophila melanogaster was studied using the 'maternal effects approach'. Basc males were irradiated in N2, air or O2 either as 48-h-old pupae (to sample spermatids) or as 3-4-day-old adults (to sample mature spermatozoa) and mated to females of 3 repair-deficient strains (mei-9a: excision-repair-deficient; mei-41D5: post-replication-repair-deficient; mus(1)101D1: post-replication-repair-deficient and impaired in DNA synthesis). Simultaneous controls involving mating of males to repair-proficient females (mei+) were run. The frequencies of sex-linked recessive lethals and of autosomal translocations were determined following standard genetic procedures. The responses elicited in the different crosses with repair-deficient females were compared with those in mei+ crosses. The main findings are the following: with mei-9 females, the frequencies of recessive lethals are higher after irradiation of spermatids in N2, but not after irradiation in air of O2 (relative to those in the mei+ crosses); this result is different from that obtained in earlier work with spermatozoa, in which cell stage, higher yields of recessive lethals were obtained after irradiation of males in either N2 or air; in the mei-9 crosses, there are no significant differences in response (relative to mei+) after irradiation of either spermatozoa or spermatids in O2; the translocation frequencies in the mei-9 crosses are similar to those in the mei+ crosses, irrespective of the treated germ cell stage or the irradiation atmosphere; irradiation of either spermatozoa or spermatids in N2, air or O2 does not result in any differential recovery of recessive lethals in the mei-41 relative to mei+ crosses; irradiation of spermatids in N2 and of spermatozoa in air leads to a higher recovery of translocations in the mei-41 crosses; and after irradiation of spermatids or spermatozoa in any of the gaseous atmospheres, the frequencies of recessive lethals and of translocations are lower in the mus-101 crosses. The differences in responses (between cell stages, in different gaseous atmospheres and with different repair-deficient females) are explained on the basis of both qualitative and quantitative differences in the composition of the initial lesions and the extent to which their repair may be affected by the defects present in the different repair-deficient females. Several discrepancies between expectations based on biochemical results and the genetic results are pointed out.(ABSTRACT TRUNCATED AT 400 WORDS)     

Isolation and Characterization of X-Linked Mutants of DROSOPHILA MELANOGASTER Which Are Sensitive to Mutagens

Thirteen X-linked mutants have been isolated in Drosophila melanogaster which render male and homozygous female larvae sensitive to the mutagen methyl methanesulfonate. Their characterization and preliminary assignment to functional groups is described. Four of these mutants are alleles of mei-41 (Baker and Carpenter 1972). Like previously isolated alleles of this locus, these mutants reduce fertility and increase loss and nondisjunction of the X-chromosome in homozygous females. The remaining mutants have been tentatively assigned to six functional groups (two mutants to the mus(1)101 locus, two to mus(1)102 , two to mus(1)103, and one each to mus(1)104, mus(1)105 , and mus(1)106). Several of the complementation groups can be distinguished on the basis of nondisjunction and cross sensitivity to mutagens. Females homozygous for the mei-41, mus(1)101 and mus(1)102 mutants exhibit elevated levels of nondisjunction. Mutants belonging to complementation groups mei-41, mus(1)101, and mus(1)104 are sensitive to nitrogen mustard (HN2) in addition to their MMS sensitivity. Among these mutants there is currently a direct correlation between sensitivity to HN2, sensitivity to 2-acetylaminofluorene and a deficiency in post-replication repair ( Boyd and Setlow 1976). Only the mei-41 mutants are hypersensitive to UV radiation, although several of the mutants exhibit sensitivity to gamma-rays. Semidominance is observed in female larvae of the mei-41, mus(1)104, and mus(1)103 mutants after exposure to high concentrations of MMS. The properties of the mutants generally conform to a pattern which has been established for related mutants in yeast. Additional properties of these mutants are summarized in Table 9.     

Studies on mutagen-sensitive strains of Drosophila melanogaster. II. Detection of qualitative differences between genetic damage induced by X-irradiation of mature spermatozoa in oxygenated and anoxic atmospheres through the use of the repair-deficient mutant mei-9a

Muller-5 males were irradiated with X-rays in nitrogen, in air or in oxygen (followed by nitrogen or oxygen post-treatments in the nitrogen and oxygen series) and were mated to females of a repair-proficient strain (mei+) or to those of a strain known to be deficient in excision repair of UV damage (in somatic cells). The latter strain, designated as mei-9a, is also known to be sensitive, in the larval stages, to the killing effects of UV, X-rays and to a number of chemical mutagens. The frequencies of sex-linked recessive lethals and autosomal translocations induced in the spermatozoa of males were determined and compared. The frequencies of sex-linked recessive lethals in the mei-9 control groups were consistently higher than in the mei+ groups. Irradiation in air or in nitrogen led to significantly higher yields of recessive lethals when the irradiated males were mated to mei-9 females, whereas, after irradiation in oxygen, the yields were similar with both kinds of female. No significant differences in the frequencies of reciprocal translocations were observed between the mei+ and mei-9 groups after irradiation of the males in nitrogen, in air or in oxygen. Likewise, no differential effects of the contrasting post-treatments (nitrogen versus oxygen), either for recessive lethals or for translocations, could be discerned. These results are considered to support the notion that the kinds of genetic damage induced in mature spermatozoa in air or in nitrogen are qualitatively similar (at least with respect to the component(s) that lead to the production of recessive lethal mutations), but clearly different when induced in an oxygen atmosphere. The enhanced yields of recessive lethals with mei-9 females (after irradiation of the males either in air or in nitrogen) has been interpreted on the assumption that the mei-9 mutant is also deficient for the repair of X-ray-induced, recessive lethal-generating premutational lesions. Possible reasons for the lack of differences between the mei+ and mei-9 groups with respect to translocation yields and for the absence of measurable differences in response between the contrasting post-treatments (after irradiation of the males in nitrogen) are discussed.     

Genetic study on the effects of the repair-deficient mutant females mei-9a, mei-41D5, mus101D1, mus104D1 and mus302D1 of Drosophila on spontaneous and X-ray-induced chromosome loss in the paternal genome

The repair-deficient mutants mei-9a, mei-41D5, mus101D1, mus104D1 and mus302D1 in Drosophila melanogaster were investigated regarding their effects on spontaneous and X-ray-induced chromosome loss in postmeiotic cells. Each mutant was incorporated singly into XC2, and the ring-X male provided with BSYy+. From matings of males carrying mus101D1, mus302D1 or mei-41D5, mutants identifying a caffeine-sensitive (CAS) postreplication-repair pathway, with corresponding mutant females, and non-mutant males to non-mutant females, overall frequencies of spontaneous partial loss and spontaneous complete loss were significantly increased in each mutant cross except for spontaneous complete loss with mus302 where an increase was noted only in brood 2. Similar findings were noted when males carrying the excision-repair mutant mei-9a were mated with mei-9a females. Males carrying the mutant mus104D1, identifying a caffeine-insensitive (CIS) postreplication-repair pathway, tested with mus104D1 females, produced results that were not significantly different from non-mutant controls. When males were given 3000 rad X-irradiation, frequencies of induced partial loss were significantly higher with mus101D1, mus302D1, mei-41D5 and mei91, and not significantly higher with mus101D1, mus302D1, mei41D5 and mei-9a, and not significantly different from controls with mus104D1. It was suggested that the functional CAS postreplication-repair pathway primarily promotes repair of breaks while an alternative pathway(s) not defined by mus104 promotes misrepair. Therefore, the significant increases in both spontaneous and induced partial loss with the excision-repair-deficient mutant mei-9a suggests the possibility that (a) the excision-repair-pathway may not function in misrepair and (b) the undefined misrepair pathway may be dominant pathway for postreplication repair in Drosophila since mei-9a females presumably have functional postreplication repair and misrepair capacity. The suggestion that the CAS postreplication-repair pathway and the excision-repair pathway function primarily in repair, and an undefined pathway in misrepair is in line with the finding that with mus104D1, no significant increase was found in spontaneous complete loss, but with mus101D1, mus302D1, mei-41D5 and mei-9a significant increases were observed. Results on induced complete loss, with the exception of those with mei-41D5, show a poor correlation with other classes of loss of each of the mutants. Possible explanations for this discrepancy are discussed.     

Postreplication repair-defective mutants of Drosophila melanogaster fall into two classes

Summary Primary cell cultures derived from embryos of a control stock of Drosophila melanogaster respond to ultraviolet light within the first hour after exposure with a decline in thymidine incorporation and a decline in the ability to form newly synthesized (nascent) DNA in long segments. Cells derived from two nonallelic excision-defective mutants (mei-9 and mus201) exhibit the same quantitative decline in both phenomena as do control cells. In contrast, cells from five nonallelic postreplication repair-defective mutants (mei-41, mus101, mus205, mus302 and mus310) respond to ultraviolet light by synthesizing nascent DNA in abnormally short segments. Two of these five mutants (mus302 and mus310) also exhibit unusually low thymidine incorporation levels after irradiation, whereas the other three mutants display the normal depression of incorporation.These results indicate that excision repair does not influence the amount or the length of nascent DNA synthesized in Drosophila cells within the first hour after exposure to ultraviolet light. Of the five mutations that diminish postreplication repair, only two reduce the ability of irradiated cells to synthesize normal amounts of DNA.Abbreviation used UV ultraviolet light — principal wavelength 254 nm     

Genetic analysis of X-linked mutagen-sensitive mutants of Drosophila melanogaster

Mutants at 2 new loci which control mutagen-sensitivity are described. Mutants at both loci are female-sterile and are hypersensitive to killing by MMS; neither increases the frequency of sex-linked recessive lethals. A screen of previously described female-sterile and meotic mutants has revealed that a number of these are also sensitive to mutagens. In addition, several new mutants have been identified on the basis of sensitivity to either HN2 or MMS. An anlysis of complementation data suggests that all of the X-linked genes controlling sensitivity to MMS may now have been identified. Among the new mei-41 alleles are mutants which show verly little meiotic nondisjunction or loss. Cytogenetic mapping of previously known mutants is also described. The mutants mus(1)104^D1 and mei-41^D5 are located in th eregion 14B13±?14D1,2 on the polytene chromosome map, and they map very close to each other genetically. Cytogenetically mus(1)101^D1 is between salivary chromosome bands 12A6,7 and 12D3, mus(1)103^D1 is between bands 12A1,2 and 12A6,7, and mus(1)-109^A1 is in section 8F3-9A2.     

The influence of gamma-irradiation in low doses on the rate of dominant lethal mutations in drosophila melanogaster

The dose-rate effect of acute and chronic irradiation in the dose of 0.2 Gy in Drosophila melanogaster repair (mei-41, mus209 [Russian character: see text] mus309) and free radicals detoxication (sod) mutant strains was investigated. Was shown the lack of dose rate effect on the rate of dominant lethal mutations in mei-41, mus209 and sod. However in mus309, that has defect in the main Drosophila pathway of the DNA double strand breack repair, the increase of the mutation rate after chronic irradiation was observed (inverse dose-rate effect). The obtained results suggest the main role of DNA double strand breack repair in dose-rate effect formation in Drosophila.     

Mutations at the mei-41, mus(1)101, mus(1)103, mus(2)205 and mus(3)310 loci of Drosophila exhibit differential UDS responses with different DNA-damaging agents

5 mutagen-sensitive mutants of Drosophila melanogaster, reported to perform normal or only slightly reduced excision repair of UV damage, were examined by an unscheduled DNA synthesis (UDS) assay. This assay measures the ability of cultured primary cells, derived from each mutant, to perform the resynthesis step in the excision repair pathway, following damage to cellular DNA by direct-acting alkylating agents, UV or X-irradiation. 2 mutants, classified as completely or partially proficient for both excision and postreplication repair of UV damage, mus(1)103 and mus(2)205, were found to give positive UDS responses only for UV damage. These mutants exhibit no measurable UDS activity following DNA damage by several different alkylating agents and X-rays. 3 mutants, classified as having no defect in excision repair, but measurable defects in postreplication repair of UV damage, mei-41, mus(1)101, and mus(3)310 exhibit 3 different response patterns when tested with the battery of agents in the UDS assay. The mutant mei-41 exhibits a highly positive UDS response following damage by all agents, consistent with its prior classification as excision-repair-proficient, but postreplication-repair-deficient for UV damage. The mutant mus(1)101, however, exhibits a strong positive UDS response following only UV damage and appears to be blocked in the excision repair of damage produced by both alkylating agents and X-irradiation. Finally, mus(3)310 exhibits no UDS response to alkylation, X-ray or UV damage. This is not consistent with its previous classification. Results obtained with the quantitative in vitro UDS assay are entirely consistent with the results from two separate in vivo measures of excision repair deficiency following DNA damage, larval hypersensitivity to killing and hypermutability in the sex-linked recessive lethal test.     

Hypersensitivity of Drosophila mei-41 mutants to hydroxyurea is associated with reduced mitotic chromosome stability

6 mutant alleles of the mei-41 locus in Drosophila melanogaster are shown to cause hypersensitivity to hydroxyurea in larvae. The strength of that sensitivity is directly correlated with the influence of the mutant alleles on meiosis in that: alleles exhibiting a strong meiotic effect (mei-41D2, mei-41D5, mei-41D7) are highly sensitive; alleles with negligible meiotic effects (mei-41(104)D1, mei-41(104)D2) are moderately sensitive and an allele which expresses meiotic effects only under restricted conditions (mei-41D9) has an intermediate sensitivity. This sensitivity is not a general feature of strong postreplication repair-deficient mutants, because mutants with that phenotype from other loci do not exhibit sensitivity (mus(2)205A1, mus(3)302D1, mus(3)310D1). The observed lethality is not due to hypersensitivity of DNA synthesis in mei-41 larvae to hydroxyurea as assayed by tritiated thymidine incorporation. Lethality is, however, potentially attributable to an abnormal enhancement of chromosomal aberrations by hydroxyurea in mutant mei-41 larvae. Both in vivo and in vitro exposure of neuroblast cells to hydroxyurea results in an increase in 3 types of aberrations which is several fold higher in mei-41 tissue. Since hydroxyurea disrupts DNA synthesis, these results further implicate the mei-41 locus in DNA metabolism and provide an additional tool for an elucidation of its function. The possible existence of additional genes of this nature is suggested by a more modest sensitivity to hydroxyurea which has been detected in two stocks carrying mutagen-sensitive alleles of alternate genes.     

Studies on mutagen-sensitive strains of Drosophila melanogaster. VI. The effect of DNA-repair deficiencies in spermatids, spermatocytes and spermatogonia irradiated in N2 or O2

This study was aimed at ascertaining the extent to which paternal repair processes possibly deficient in mei-9a, mei-41D5 and mus-101D1 genotypes would affect the recovery of radiation-induced recessive lethals in early spermatids, spermatocytes and spermatogonia. These germ cell stages were sampled in two 2-day broods from freshly hatched males, that were irradiated as 24-h old pupae in O2, or N2 followed by N2 or O2 post-treatment. Spontaneous mutation frequencies were higher in mei-9 and mei-41 males, and thus appropriate corrections were applied to the radiation data. Only with mei-9 males a clear and consistent increase of the radiation-induced mutation frequency was observed. The effect is somewhat more pronounced in brood B, presumably representing spermatogonia, than in brood A and is observed after radiation in either O2 or N2. The paternal repair process thus differs from the maternal one in that it also responds to radiation damage induced in O2. The finding that, following irradiation under anoxia, post-treatment with O2 (versus that with N2), also lowers the mutation frequency in mei-9 males, indicates that the repair defect in mei-9 does not interfere with oxygen-dependent post-radiation repair. Thus there are two different paternal repair processes in these early stages of spermatogenesis: that is, one controlled by mei-9 and one depending on oxygen. Mei-41 and mus-101 do not appear to interfere with the paternal repair process. The frequency of translocations recovered from these stages was likewise not affected by mus-101.     

The relationship between reaction kinetics and mutagenic action of monofunctional alkylating agents in higher eukaryotic systems. IV. The effects of the excision-defective mei-9L1 and mus(2)201D1 mutants on alkylation-induced genetic damage in Drosophila

Repair-defective mutants of Drosophila melanogaster which identify two major DNA excision repair loci have been examined for their effects on alkylation-induced mutagenesis using the sex-linked recessive lethal assay as a measure of genotoxic endpoint. The alkylating agents (AAs) chosen for comparative analysis were selected on the basis of their reaction kinetics with DNA and included MMS, EMS, MNU, DMN, ENU, DEN and ENNG. Repair-proficient males were treated with the AAs and mated with either excision-defective mei-9L1 or mus(2)201D1 females or appropriate excision-proficient control females. The results of the present work suggest that a qualitative and quantitative relationship exists between the nature and the extent of chemical modification of DNA and the induction of of genetic alterations. The presence of either excision-defective mutant can enhance the frequency of mutation (hypermutability) and this hypermutability can be correlated with the Swain-Scott constant S of specific AAs such that as the SN1 character of the DNA alkylation reaction increases, the difference in response between repair-deficient and repair-proficient females decreases. The order of hypermutability of AAs with mei-9L1 relative to mei-9+ is MMS greater than MNU greater than DMN = EMS greater than iPMS = ENU = DEN = ENNG. When the percentage of lethal mutations induced in mei-9L1 females are plotted against those determined for control females, straight lines of different slopes are obtained. These mei-9L1/mei-9+ indices are: MMS = 7.6, MNU = 5.4, DMN = 2.4, EMS = 2.4 and iPMS = ENU = DEN = ENNG = 1. An identical order of hypermutability with similar indices is obtained for the mus(2)201 mutants: MMS(7.3) greater than MNU (5.4) greater than EMS(2.0) greater than ENU(1.1). Thus, absence of excision repair function has a significant effect on mutation production by AAs efficient in alkylating N-atoms in DNA but no measurable influence on mutation production by AAs most efficient in alkylating O-atoms in DNA. The possible nature of these DNA adducts has been discussed in relation to repair of alkylated DNA. In another series of experiments, the effect on alkylation mutagenesis of mei-9L1 was studied in males, by comparing mutation induction in mei-9L1 males vs. activity in Berlin K (control). Although these experiments suggested the existence of DNA repair in postmeiotic cells during spermatogenesis, no quantitative comparisons could be made.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evaluation of effects of gamma-irradiation at low doses on repair and meiotic recombination mutants of Drosophila melanogaster

A comparative study of the effects of gene mutations mus209, mus309, mei-41 and rad54 of Drosophila melanogaster on the sensitivity to low-level exposure of different duration was carried out. Taken into account was the survival rate at different stages of ontogeny, female fecundity, the frequency of dominant lethal mutations (DLM) and the DNA damage. mei-41 and rad-54 mutants were most sensitive to the action of low dose radiation (80 mGy) in terms of survival and DLM. However, at the level of DNA damage, an increased radiosensitivity is observed only at larger doses of low intensity irradiation. Based on these observations, we can conclude about the importance of repair and its genes in the formation of the effect of low level doses of ionizing radiation in Drosophila.     

Induction of mutations in unirradiated X-chromosome of Drosophila melanogaster hybrids of repair deficient females mei-41 [D5] and mus209 [B1] and irradiated males M5

It has been analyzed the frequency of the recessive lethal mutations in the unirradiated X-chromosome of Drosophila. Females of wild type (CS) as well as of error-prone (mei-41) and error-free (mus209) mutant strains were used. In CS hybrids the increasing of the mutation rate (p < 0.05) was found. In muc209 hybrids the mutation rate was not affected. In mei-41 hybrids the tendency to decreasing of the mutation rate was found. The obtained results demonstrate the possible role of error-prone repair in the inducing of mutations in the unirradiated X-chromosome in the presence of irradiated homologue.     

A large-scale screen for mutagen-sensitive loci in Drosophila

In a screen for new DNA repair mutants, we tested 6275 Drosophila strains bearing homozygous mutagenized autosomes (obtained from C. Zuker) for hypersensitivity to methyl methanesulfonate (MMS) and nitrogen mustard (HN2). Testing of 2585 second-chromosome lines resulted in the recovery of 18 mutants, 8 of which were alleles of known genes. The remaining 10 second-chromosome mutants were solely sensitive to MMS and define 8 new mutagen-sensitive genes (mus212-mus219). Testing of 3690 third chromosomes led to the identification of 60 third-chromosome mutants, 44 of which were alleles of known genes. The remaining 16 mutants define 14 new mutagen-sensitive genes (mus314-mus327). We have initiated efforts to identify these genes at the molecular level and report here the first two identified. The HN2-sensitive mus322 mutant defines the Drosophila ortholog of the yeast snm1 gene, and the MMS- and HN2-sensitive mus301 mutant defines the Drosophila ortholog of the human HEL308 gene. We have also identified a second-chromosome mutant, mus215(ZIII-2059), that uniformly reduces the frequency of meiotic recombination to <3% of that observed in wild type and thus defines a function required for both DNA repair and meiotic recombination. At least one allele of each new gene identified in this study is available at the Bloomington Stock Center.     

The mutational spectrum of procarbazine in Drosophila melanogaster.

The antineoplastic agent Procarbazine was tested for the induction of genetic damage in Drosophila melanogaster. The compound was administered to adult males by oral application. The following types of genetic damage were measured: (1) sex-linked recessive lethals; (2) dominant lethals; (3) total and partial sex-chromosome loss; and (4) translocations. Procarbazine is highly mutagenic in causing recessive lethal mutations in all stages of spermatogenesis. In sperm a clear-cut concentration-effect relationship is not apparent, but in spermatids such a relationship is obtained for mutation induction at low levels of procarbazine exposure, while at high concentrations the induction of recessive lethals is not a function of concentration. A low induction of total sex-chromosome loss (X,Y) and dominant lethals was observed in metabolically active germ cells (spermatids), but procarbazine failed to produce well-defined breakage events, such as partial sex-chromosome loss (YL,YS) and II-III translocations. The results obtained in Drosophila melanogaster are discussed and compared with the mutational pattern reported in the mouse after procarbazine treatment.     

P transposition in Drosophila provides a new tool for analyzing postreplication repair and double-strand break repair.

A genetic screen has been developed in Drosophila for identifying host-repair genes responsible for processing DNA lesions formed during mobilization of P transposable elements. Application of that approach to repair deficient mutants has revealed that the mei-41 and mus302 genes are necessary for recovery of P-bearing chromosomes undergoing transposition. Both of these genes are required for normal postreplication repair. Mutants deficient in excision repair, on the other hand, have no detected effect on the repair of transposition-induced lesions. These observations suggest that P element-induced lesions are repaired by a postreplication pathway of DNA repair. The data further support recent studies implicating double-strand DNA breaks as intermediates in P transposition, because the mei-41 gene has been genetically and cytologically associated with the repair of interrupted chromosomes. Analysis of this system has also revealed a striking stimulation of site-specific gene conversion and recombination by P transposition. This result strongly suggests that postreplication repair in this model eukaryote operates through a conversion/recombination mechanism. Our results also support a recently developed model for a conversion-like mechanism of P transposition (Engels et al., 1990). Involvement of the mei-41 and mus302 genes in the repair of P element-induced double-strand breaks and postreplication repair points to a commonality in the mechanisms of these processes.