Pyrimidine auxotrophy and the complementation map of the Rudimentary locus of Drosophila melanogaster

Summary The complementation pattern of twelve rudimentary mutations has been analyzed at two different levels. When analyzed on the basis of complementation for a wing abnormality the mutations can be divided into three groups, each of which is believed to affect the activity of one of the first three enzymes of pyrimidine synthesis (Norby, 1973; Jarry and Falk, 1974; Rawls and Fristrom, 1975). However, when the mutants are analyzed for complementation on the basis of a second phenotype, pyrimidine auxotrophy, the distinction between two of these three groups is not evident. The disparity in the two patterns probably reflects a different threshold of gene activity required for the detection of an auxotrophic phenotype as compared to that at which a wing abnormality is detectable.The biochemical basis of these results is interpreted in light of recent data suggesting that at least the first two enzymes of pyrimidine synthesis are contained within a single multifunctional protein complex (Soderholm et al., 1975).     

The action of the Notch locus in Drosophila melanogaster

Summary It is shown that the Notch⁸ deficiency in Drosophila melanogaster affects a number of enzyme activities localized in the mitochondria, such as NADH oxidase (activity of the complete respiratory chain), NADH dehydrogenase (the first step in the respiratory chain before transfer to ubiquinone), Succinate dehydrogenase and -Glycerophosphate dehydrogenase. The experiments reported here do not exclude the possibility of involvement of other genes in the deficiency. The effect of duplications of the Notch locus on NADH oxidase and NADH dehydrogenase suggest that this locus determines the enzyme activities.The dosage effects of the Notch locus on activity suggest that this locus contains the structural genes for these enzymes.     

Functional diversity within the rudimentary locus of Drosophila melanogaster

Summary The rudimentary locus of Drosophila melanogaster is shown to be at least bifunctional. Mutants in different regions of the locus have either no CPSase or no ATCase activity; some mutants lack both activities. The results are discussed in correlation with the complementation and genetic map of the locus.Supported by National Research Council of Canada, grant A-1764 and National Cancer Institute of Canada, grant 6051 to D. T. Suzuki.Researcher, Centre National de la Recherche Scientifique, France and recipient of European Molecular Biology Organization Fellowship.     

EMS-induced reversion studies in the white locus of Drosophila melanogaster

5 white-locus mutants of Drosophila melanogaster, representing 5 different sub-sites, were treated with EMS and tested for reversion to wild-type. 4 of them were genuine mutants and one was not. Moreover, the ability of the 4 mutants to revert to wild-type differed from one another which therefore reflects a qualitatively distinct alteration in the genetic material delimited by each mutant.     

Suppressible P-element alleles of the vestigial locus in Drosophila melanogaster

Summary A series of P-element insertion mutations at one site in the vestigial (vg) locus was tested for cytotype dependent effects on vg expression. The mutant phenotypes for four P-element vg alleles were suppressed when the alleles were stabilized in the P-cytotype. The suppression was observed whenever repressor-producing P-elements were present in the genome. Genetic and molecular analysis indicated that the suppression is not due to excision or other irreversible alterations of the inserts. The results are consistent with a model in which somatic P-element repressor binding to the ends of P-element inserts can modify the effects of these inserts on target gene expression.     

Genetic characterization of the mei-41 locus in Drosophila melanogaster

Summary The mutagen-sensitive mutant mus(1)104 ^D1 of Drosophila melanogaster maps to a position on the X chromosome very close to the meiotic mutant mei-41 ^D5 . Both mutants have been characterized as mutagen-sensitive and defective in post-replication repair. In the present report we show by complementation studies that mus(1)104 and mus(1)103 are allelic with mei-41. In addition, two reported alleles of mus(1)104 lie between the mei-41 alleles A10 and D5. The size of the mei-41 locus is estimated to be about 0.1 centimorgans (cM). Because several alleles of mei-41 have been shown to reduce recombination and increase meiotic chromosome loss and nondisjunction, mus(1)104 ^D1 females were examined for defects in meiosis. Although there was no evidence for reduced recombination on the second chromosome in homozygous mus(1)104 ^D1 females, heterozygous mus(1)104 ^D1 /mei-41 ^>D5 and mus(1)104 ^D1 /deficiency females showed reduced levels of recombination. However, there was no evidence of an increase in nondijunction in these females.We dedicate this article to the memory of Larry Sandler, who passed away suddenly on February 7, 1987     

Region-specific aldehyde oxidase activity in Tumorous-head eye discs of Drosophila melanogaster

Summary Histochemical staining for aldehyde oxidase in mature tumorous-head eye imaginal discs of Drosophila melanogaster reveals region-specific enzyme activity that normally is not found in wild type eye discs. Confined primarily to the central portion of the mutant disc is a morphologically distinct area that can be predicted to be the only aldehyde oxidase (aldox) positive tissue in the eye disc. Prior to staining, this area can be removed mechanically from the surrounding tissue and is characterized by smooth boundaries. The separated tissue stains for aldehyde oxidase whereas the remaining disc is aldox negative as in the wild type. We presume that the aldehyde oxidase positive region subsists in the primordium of the tumorous-head abnormality and propose that the appearance of this enzyme signals a change in the state of determination in the mutant disc.     

Study of the ref(2)P locus of Drosophila melanogaster

The ref(2)P gene of Drosophila melanogaster is implicated in sigma rhabdovirus multiplication. Two common alleles of ref(2)P are known, ref(2)P ⁰ which permits sigma virus multiplication and ref(2)P ^pwhich is restrictive for most sigma virus strains. This gene maps to the cytogenetic region 37E3-F3. Using Df(2L)E55 (=Df(2L)37D2-El;37F5-38A1), we have screened for lethal, semi-lethal and visible mutations following diepoxybutane (DEB) or ethyl methanesulfonate (EMS) mutagenesis. Our data confirm than DEB is mor efficient than EMS at inducing deletions. The mutations obtained in this region define 14 complementation groups. One of them, l(2)37Dh, appears to be a general enhancer of Minute and Minute-like mutations. None of the mutations were allelic to the ref(2)P locus. Loss-of-function alleles of ref(2)P (called null) were selected following DEB mutagenesis. Homozygous or hemizygous ref(2)P ^nullflies are male sterile. These flies, like homozygous or hemizygous ref(2)P ⁰flies, are fully permissive for sigma virus replication. We suggest that the ref(2)P products interact with viral products, but that this interaction is not necessary for an efficient viral cycle.     

Genetic instability at the cut locus of Drosophila melanogaster induced by the MR-h12 chromosome

Summary Unstable mutations were generated at the cut locus by the MR-h12 factor which induces male recombination. The unstable allele ct ^MR2, containing the MR-transposon in the cut locus is a very powerful mutator producing a number of different viable and lethal mutations both in the cut locus and outside it.I describe several types of mutations: stable reversion to wild type, which were sometimes associated with the appearance of unstable mutations in other loci; of stable deficiencies at the cut locus (lethals); new unstable mutations at different loci with the ct ^MR2 allele conserved; new unstable cut alleles with a phenotype other than that of ct ^MR2. The possible mechanisms of these mutational events are discussed. The genetic system constructed in the present work affords an opportunity for molecular studies of the cut locus and the MR-transposon, as a sequence from the cut locus has recently been cloned (Tchurikov et al. 1981).     

Genetic localization of a follicle cell protein locus in Drosophila melanogaster

Summary Three variant forms of a novel set of follicle cell proteins (Fc) were found when screening geographic wild-type strains of Drosophila melanogaster by SDS-polyacrylamide gel electrophoresis of ³⁵S-methionine labelled ovaries. These variant forms were used to establish X chromosomal linkage and for further genetic localization by both recombinant analysis and by cytogenetical mapping. A locus involved in the synthesis of Fc proteins was localized to the 7C1-9 region, i.e. very close to the singed locus (21.0 cM). The number of Fc proteins, their variation and possible function is discussed.     

Genetic instability in Drosophila melanogaster

Summary An unstable long tandem duplication which includes the white locus twice, marked with w ^sp in the left and w ^17G in the right locus, when kept in males has been found to produce red-eyed sons which have lost the long duplication and with it the w ^sp and w ^17G mutants. Such exceptions were produced also when w ^17G had been exchanged for w ^a.Stocks originating from these exceptions are unstable, producing: 1) zeste males, also unstable, 2) w ^- deletions, stable, 3) transpositions of the white locus to sites in other chromosomes.The instability is interpreted as the effect of an IS element, within or adjacent to the white locus, which is supposed to retain a duplication of the proximal zeste interacting part of this locus. According to the orientation of the IS element the duplicated part can be active or inactive, giving a zeste or red eye phenotype.The frequency of exceptional offspring after X-ray treatment of the red and zeste unstable stocks have been compared to stable stocks with corresponding genotypes.     

Dopa decarboxylase from Drosophila melanogaster

Summary Dopa decarboxylase (EC 4.1.1.26) has been purified to near homogeneity from mature larvae of Drosophila melanogaster. The enzyme has a molecular weight of 113,000 measured by sucrose gradient sedimentation and 102,000 measured by variable porosity acrylamide gel electrophoresis. Electrophoresis under denaturing conditions revealed the enzyme consists of two subunits of molecular weight 54,000. The affinity of the enzyme for L-dopa is 30-fold greater than for L-tyrosine. Activity is strongly inhibited by heavy metal ions and the sulfhydryl reagent N-ethylmaleimide. N-acetyl dopamine acts as a competitive inhibitor of the enzyme.Antibodies were elicited against the purified enzyme and measurements of the amount of cross-reacting material (CRM) in two groups of mutants were made. The first group comprised the recessive lethal mutants l(2)amd. Heterozygous mutant stocks are hypersensitive to -methyl dopa, an inhibitor of dopa decarboxylase. These stocks were found to have nearly normal amounts of CRM and enzyme activity.A second group of recessive lethal mutants, characterized by lower levels of dopa decarboxylase, was also analysed. These mutants, designated l(2) Ddc, as heterozygotes exhibited CRM levels between 25 and 75% of normal. Although they are alleles at a single locus, they were classifiable into three distinct groups whose properties readily could be ascribed to a homodimeric structure of the enzyme. This structure would also account for the pattern of intracistronic complementation exhibited by the mutants. Finally, the severity of the mutant defects, as judged by our measurements of CRM and activity, closely parallels that deduced from their complementation pattern. We conclude that these mutations are lesions in the structural gene for dopa decarboxylase.     

Nucleotide metabolism variability in Drosophila melanogaster

Summary We have studied the metabolic variability within different wild-type strains of Drosophila melanogaster for resistance to antimetabolites (aminopterin, 8-azaguanine), the target enzymatic activities (dihydrofolate reductase, hypoxanthine guanine phosphoribosyltransferase) and capacity to survive on minimal medium with or without exogenous bases or nucleosides (thymidine, hypoxanthine). No correlation was found between dihydrofolate reductase activity and resistance to aminopterin. The results indicated the importance of salvage pathways in the resistance mechanisms in Drosophila.     

The dominant Drop eye mutations of Drosophila melanogaster define two loci implicated in normal eye development

The three existing dominant gain-of-function Drop alleles, Dr ¹, Dr ^Mio and Dr ^We , previously assumed to define a single locus, severely disrupt eye development. Genetic analysis of ethylmethanesulphonate (EMS) and irradiation-induced revertants revealed that the Drop mutations define two loci: the Drop locus, which is defined by the Dr ¹ and Dr ^Mio mutants, and a separate locus defined by the Dr ^We mutation, which has been renamed Wedge. The majority of the Dr ¹ and Dr ^Mio revertants are embryonic lethal in trans, mutant embryos exhibiting trachea that fail to join the Filzkörper, thus revealing a role for the Drop gene in embryogenesis. Clonal analysis of lethal revertant alleles suggests a role for both genes in eye development. In the Drop homozygous mutant clones, the outer photoreceptor cells R1–R6 develop aberrantly. Wedge, however, is not required by the developing photoreceptor cells but its absence does disrupt normal ommatidial alignment. Although the Drop and nearby string loci were shown to be genetically distinct, both Dr ¹ and Dr ^Mio were found to interact in trans with lesions at the string locus, causing loss and derangement of bristles and loss of neuromuscular coordination.