Transposon-induced symbiotic mutants of Bradyrhizobium japonicum: isolation of two gene regions essential for nodulation

Summary Two strains of the soybean endosymbiont Bradyrhizobium japonicum, USDA 110 and 61 A101 C, were mutagenized with transposon Tn5. After plant infection tests of a total of 6,926 kanamycin and streptomycin resistant transconjugants, 25 mutants were identified that are defective in nodule formation (Nod^-) or nitrogen fixation (Fix^-). Seven Nod^- mutants were isolated from strain USDA 110 and from strain 61 A101 C, 4 Nod^- mutants and 14 Fix^- mutants were identified. Subsequent auxotrophic tests on these symbiotically defective mutants identified 4 His^- Nod^- mutants of USDA 110. Genomic Southern analysis of the 25 mutants revealed that each of them carried a single copy of Tn5 integrated in the genome. Three 61 A101 C Fix^- mutants were found to have vector DNA co-integrated along with Tn5 in the genome. Two independent DNA regions flanking Tn5 were cloned from the three nonauxotrophic Nod^- mutants and one His^-Nod^- mutant of USDA 110. Homogenotization of the cloned fragments into wild-type strain USDA 110 and subsequent nodulation assay of the resulting homogenotes confirmed that the Tn5 insertion was responsible for the Nod^- phenotype. Partial EcoR1 restriction enzyme maps around the Tn5 insertion sites were generated. Hybridization of these cloned regions to the previously cloned nod regions of R. meliloti and nif and nod regions of B. japonicum USDA 110 showed no homology, suggesting that these regions represent new symbiotic clusters of B. japonicum.     

Suppression of temperature sensitive mutants of bacteriophage T4 by bacterial opal suppressors

Summary Some of the partial revertants from opal (UGA) mutants of bacteriophage T4 are temperature sensitive in su ^– host cells but are still temperature resistant in su ⁺ cells. Hence these revertants are missense mutants suppressible by bacterial opal suppressors. Such a suppression may be explained in terms of codon-anticodon interactions by the wobble hypothesis.     

Oo mutations in the galactose operon in E. coli

Summary Eleven mutants lacking the three enzymes of galactose fermentation were investigated.Eight of the mutants revert spontaneously to the Gal ⁺ phenotype. These cannot be deletions. Six of these spontaneously reverting mutants do not respond to the mutagens 2-aminopurine, ethyl-methanesulfonate and N-Methyl-N-Nitro-N-nitrosoguanidine. It is concluded that these o ^o mutations cannot be reverted by base substitution.The eleven o ^o mutants are not of the amber or ochre type as shown by their behaviour towards suppressor genes.The possible nature of the mutations is discussed.     

Biochemical studies of H-2K antigens from a group of related mutants. I. Identification of a shared mutation in B6-H-2 bm5 and B6-H-2 bm16

Structural studies of the H-2 gene products from a group of five closely related but independent C57BL/6 H-2 mutant mice were undertaken. Each of the mutants exhibits reciprocal graft rejection with the parent. The group is remarkable, however, because each member of this group can accept skin grafts from any other member. The results of biochemical analysis of the H-2 glycoproteins from two of these related mutants, bm5 and bm16, are presented in this report. Evidence is given that the H-2K molecules from these two mutants are identical to each other based on comparative tryptic peptide mapping profiles with the parent. From partial amino acid sequence analysis, K products of both mutants have at least one common difference from the parental type located at residue number 116. Definitive studies established that in both bm5 and bm16 a tryosine found in the parent molecule is substituted with a phenylalanine in the mutant. These results show that a biochemical difference between the K products of the two mutants and of the parent can be detected, that the mutants appear to be identical with one another even though they arose independently, and that they differ from the other H-2K ^b mutants analyzed.Abbreviations used in this paper B6 C57BL/6Kh - bm5 B6-H-2^bm5 - bm6 B6-H-2 ^bm6 - bm7 B6.C-H-2 ^bm7 - bm9 B6.C-H-2 ^bm9 - bm16 B6-H-2 ^bm16 - D H-2D - K H-2K - MHC major histocompatibility complex     

Purine transport by Malpighian tubules of pteridine-deficient eye color mutants of Drosophila melanogaster

Uptakes of guanine into Malpighian tubules of wild-type Drosophila and the eye color mutants white (w), brown (bw), and pink-peach (p ^p) have been compared. Tubules for each of these mutants are unable to concentrate guanine intracellularly. The transport of xanthine and riboflavin is also deficient in w tubules. The transport of guanosine, adenine, hypoxanthine, and guanosine monophosphate is similar in wild-type and white Malpighian tubules. These data and other information about these mutants make it likely that these pteridine-deficient eye color mutants do not produce pigments because of the inability to transport a pteridine precursor. This view supports the hypothesis that mutants which lack both pteridine and ommochromes do so because precursors to both classes of pigments share a common transport system.This work was supported by Grant GM22366 from NIH.     

Arsenate-resistant alkaline phosphatase-constitutive mutants of Escherichia coli.

Summary When arsenate-resistant mutants are selected approximately 50 per cent of them are also consitutive for the synthesis of alkaline phosphatase and the Pi-binding protein. Some of these mutants are linked to ilv (phoS ^- or phoT ^-), others are linked to proC (phoR ^-). One of the mutant strains linked to ilv lost the Pi-binding protein (the phoS gene product). Resistance to arsenate, constitutivty for alkaline phosphatase synthesis and loss of the Pi-binding protein occurred pleiotropically by the same phoS ^- mutation.     

Pleiotropic mutations in Serratia marcescens which increase the synthesis of certain exocellular proteins and the rate of spontaneous prophage induction

Summary Mutants of S. marcescens HY have been isolated which produce between five and one hundred times more exocellular nuclease than does the parental strain. These nuclease-superactive (nuc ^su) mutants are highly pleiotropic: they produce more exocellular marcescin A and lipase than the wild-type and their ability to inactivate penicillin G is increased. Furthermore, all nuclease-superactive mutants if lysogenic for the heteroimmune phages Kappa and/or y show spontaneous induction rates for both prophages 10 to 200 fold greater than the corresponding wild-type. Nuc ^su mutants of independent origin synthesize nuclease and marcescin A in approximately proportional amounts although the corresponding structural genes do not seem to be part of a single operon because some bacteriocin-superactive mutants were isolated which showed an increase of the synthesis of marcescin A only. Nuclease-defective (nuc) mutants are all of the non-pleiotropic type. Three hypotheses to explain the effects of the nuc ^su mutation at the molecular level are discussed and some evidence in support of one of these hypotheses (gene-dosage effect) is presented in an accompanying paper (Timmis and Winkler, 1973).     

MORPHOGENESIS IN TRICHODERMA: AUTONOMOUS AND NONAUTONOMOUS PIGMENTATION IN HETEROKARYONS OF COLOR MUTANTS IN TRICHODERMA VIRIDE

The final step in the process of conidiation—conidial pigmentation—was studied in the fungus Trichoderma viride. Twenty-nine auxotrophic, color mutants, isolated from the same green wildtype strain, were paired to produce stable heterokaryons in all possible combinations and grouped according to their complementation behavior. No complementation (green pigmentation) was found in any of the heterokaryons formed by pairs of white (W) mutants. However, these mutants could be separated into two groups with respect to their behavior when paired with yellow (Y) and brown (Br) mutants. When W^c mutants were paired with any of the Y or Br mutants complementation took place. However, W^d mutants displayed this reaction with only one group of yellow mutants (Y^a) and not with the other (Y^b) nor with Br mutants. In noncomplementing heterokaryons such as Y^b/W^d, only yellow and white conidia were produced, pigmentation being autonomous. On the other hand, in heterokaryons in which complementation did take place, as for instance Y^a/W^d, green as well as white and yellow conidia were produced. Differential sensitivity to UV irradiation was used to show that the green conidia were of either W^d or F^a genotype, indicating a nonautonomous type of gene action. It is suggested that the genes W^c, Y^a, Y^b and Br have a sequential structural role in the biosynthesis of the green pigment, while W^d controls the activity of three (W^c, Y^b, Br) of these genes.     

A slow-growing, ribosomal mutant of Salmonella typhimurium

Summary The mechanisms of S. typhimurium reversion from histidine dependence (his ^–) to histidine independence (his ⁺) were studied. Genetic and phenotypic characteristics of revertants induced by nitrosoguanidine were analyzed. Among them a class of slow-growing revertants was selected. It is found that all of these slow-growing revertants carry the original UGA nonsense mutation within the histidine operon. They are streptomycin sensitive and no specific suppressor(s) for UGA nonsense codon are demonstrable. The suppression takes place in the absence of conventional nonsense UGA suppressor(s). It is seemingly due to a ribosomal mutation which in turn is likely to produce ambiguity in the process of translation and which suppresses the UGA nonsense codon. The rate of both in vivo and in vitro protein synthesis is significantly reduced. The fact that streptomycin, at sublethal doses, reduced the growth rate of these mutants, probably because of the simultaneous burden of two ambiguity factors, suggests that the mutants described may be regarded as a kind of ram (ribosomal ambiguity) mutants with a his ^– sup ^–genotype. Their capacity to translate poly-U is reduced and in that respect they differ from ram mutants of Escherichia coli.     

Mutants partially defective in excision repair at five autosomal loci in Drosophila melanogaster

Primary cell cultures derived from mutants in seventeen different genes were analyzed for their ability to excise pyrimidine dimers from DNA. Five of these mutagen-sensitive mutants [mus(2)205^A1, mus(3)302^D1, mus(3) 304^D3, mus(3)306^D1, mus(3)308^D2] display a significantly reduced excision capacity relative to control cultures. In addition, two of the five [mus(3)306^D1, mus(3)308^D2] are defective in the accumulation of single-strand breaks normally seen after ultraviolet irradiation. This study, therefore, brings the total number of Drosophila mutants known to be defective in excision repair to seven. The results are discussed relative to other genetic and biochemical properties of these mutants. This work is dedicated to Professor W. Beermann whose own contributions were instrumental in focusing a modern analysis of the eukaryotic genome on the diptera. Those of us who benefitted so much from his personal guidance recognize that we did so as a result of some sacrifice on his part. One of Boyd's contemporaries in Tübingen once remarked: “It's terrifying to think what Professor Beermann could do if he were in the lab full time.”     

Isolation of novel pre-mRNA splicing mutants of Schizosaccharomyces pombe

 New prp (pre-mRNA processing) mutants of the fission yeast Schizosaccharomyces pombe were isolated from a bank of 700 mutants that were either temperature sensitive (ts^-) or cold sensitive (cs^-) for growth. The bank was screened by Northern blot analysis with probes complementary to S. pombe U6 small nuclear RNA (sn RNA), the gene for which has a splicesomal (mRNA-type) intron. We identified 12 prp mutants that accumulated the U6 snRNA precursor at the nonpermissive temperature. All such mutants were also found to have defects in an early step of TFIID pre-mRNA splicing at the nonpermissive temperature. Complementation analyses showed that seven of the mutants belong to six new complementation groups designated as prp8 and prp10-prp14, whereas the five other mutants were classified into the known complementation groups prp1, prp2 and prp3. Interestingly, some of the isolated prp mutants produced elongated cells at the nonpermissive temperature, which is a phenotype typical of cell division cycle (cdc) mutants. Based on these findings, we propose that some of the wild-type products from these prp ⁺ genes play important roles in the cellular processes of pre-mRNA splicing and cell cycle progression. Received: 15 April 1996/Accepted: 9 July 1996     

A class of gyrase mutants of Salmonella typhimurium show quinolone-like lethality and require Rec functions for viability

We have identified a new class of DNA gyrase mutants of Salmonella typhimurium that show chronic derepression of the SOS regulon. Thus, these mutants mimic the response of wild-type cells to gyrase inhibitors of the quinolone family. SOS induction by conditional lethal mutations gyrA208 or gyrB652, like that mediated by quinolones, is completely dependent on the function of the recB gene product. Introduction of recA or recB null mutations into these strains exacerbates their temperature-sensitive phenotype and prevents growth at the otherwise permissive temperature of 37°C. Selection of suppressors that concomitantly restore growth at 37°C and SOS induction in a recB^? background yielded mutations that relieve the RecB requirement for homologous recombination; namely, sbcB mutations as well as mutations at a new locus that was named sbcE. Such mutations also restore SOS induction in quinolone-treated gyr⁺recB^? strains. These findings indicate that Rec functions are needed for growth of the gyrase mutants at 37°C and suggest that recombinational repair intermediates constitute the SOS-inducing signal in the mutants as well as in quinolone-treated wild-type bacteria. Unlike quinolones, however, the gyr mutations described in this study do not cause detectable accumulation of ‘cleavable’ gyrase–DNA complexes in plasmid or chromosomal DNA. Yet gyrA208 (the only allele tested) was found to trigger RecB-mediated reckless degradation of chromosomal DNA in recA^? cells at restrictive temperatures. Indirect evidence suggests that double-stranded DNA ends, entry sites for the RecBCD enzyme, are generated in the gyr mutants by the breakage of DNA-replication forks. We discuss how this could occur and how recombinational rescue of collapsed replication forks could account for cell survival (and SOS induction) in the gyr mutants as well as in quinolone-treated bacteria.     

Fertility-deficient E. coli K-12 mutants

Summary Fertility-deficient and f2-r mutants of E. coli K-12 were studied. The above mutants were isolated following the nitrogen-mustard treatment of the E. coli K-12 Hfr and E. coli F ¹ lac ⁺-strains. Isolation of these mutants from F ¹-strains showed that mutations occur in the F-factor no matter whether it was in autonomous state or integrated in a chromosome.The existence of mutants of two types, fertility-deficient and f2-r, was demonstrated. Type I mutants were characterized by the maintenance of a low level phage f2-adsorption activity and by a 10-fold decrease of their fertility as compared with the original strain when crossed in the liquid medium. In crosses in solid media the recombination frequency in the case of type I mutants used as donor was the same as with the original strain. Type II mutants were characterized by the entrie loss of their f2-phage adsorption ability, by a 1,000-fold decrease of fertility in liquid media, and by the inability to recombinate in solid media.     

Studies of partially repressed mutants at the tamA and areA loci in Aspergillus nidulans

Summary Mutants, designated tamA ^r, have been isolated on the basis of simultaneous resistance to toxic analogues thiourea, aspartate hydroxamate and chlorate with L-alanine as the sole nitrogen source. tamA ^r mutants are also resistant to methylammonium. This resistance of tamA ^r mutants is correlated with partially repressed activity of a number of enzyme and transport systems regulated by ammonium. Furthermore, tamA ^r mutants have low NADP-glutamate dehydrogenase (NADP-GDH) activity and also efflux ammonium under certain growth conditions.Mutants at the areA locus (areA ^r) have also been isolated on the basis of resistance to these analogues, with nitrate or L-aspartate as the nitrogen source. These, similar to tamA ^r lesions, result in resistance to methylammonium and are partially repressed for ammonium repressible systems, but in contrast to tamA ^r, areA ^r alleles have wild-type NADP-GDH activity and normal ammonium efflux. tamA ^r and areA ^r mutants grow as wild type on all nitrogen or carbon sources tested, are recessive, and appear to be epistatic to all other mutations (gdhA1, meaA8 and meaB6) which result in derepressed levels of ammonium regulated system. Whereas tamA ^r and areA ^r phenotypes are additive, tamA ^r is epistatic to areA ^d phenotype.     

Deoxyglucose mapping of nervous activity induced inDrosophila brain by visual movement

Summary Autoradiographs of the brains of the visual mutantsouter rhabdomeres absent ^JK84 (ora),small optic lobes ^KS58 (KS58) andno object fixation E ^B12 (B12) have been obtained by the deoxyglucose method. The patterns of metabolic activity in the optic lobes of the visually stimulated mutants is compared with that of similarly stimulated wildtype (WT) flies which was described in Part I of this work (Buchner et al. 1984b).In the mutantKS58 the optomotor following response to movement is nearly normal despite a 40–45% reduction of volume in the visual neuropils, medulla and lobula complex. InB12 flies the volume of these neuropils and the optomotor response are reduced. In autoradiographs of both mutants the pattern of neuronal activity induced by stimulation with moving gratings does not differ substantially from that in the WT. It suggests that only neurons irrelevant to movement detection are affected by the mutation. However, in the lobula plate of someKS58 flies and in the second chiasma of allB12 flies, the pattern of metabolic activity differs from that observed in WT flies. Up to now no causal relation has been found between the modifications described in behaviour or anatomy and those observed in the labelling of these mutants.In the ommatidia ofora flies the outer rhabdomeres are lacking while the central photoreceptors appear to be normal. Stimulus-specific labelling is absent in the visual neuropil of these mutants stimulated with movement or flicker. This result underlines the importance of the outer rhabdomeres for visual tasks, especially for movement detection.Abbreviations DG deoxyglucose - KS58 small optic lobes^KS58 - B12 no object fixation E^B12 - JK84 ora outer rhabdomeres absent ^JK84 - WT wildtype     

A Systematic Evaluation of the Function of the Protein-Remodeling Factor Hsp104 in [PSI+] Prion Propagation in S. cerevisiae by Comprehensive Chromosomal Mutations

The yeast prion [PSI⁺] represents an aggregated state of the translational release factor Sup35 (eRF3) and deprives termination complexes of functional Sup35, resulting in nonsense codon suppression. Protein-remodeling factor Hsp104 is involved in thermotolerance and [PSI⁺] propagation, however the structure-and-function relationship of Hsp104 for [PSI⁺] remains unclear. In this study, we engineered 58 chromosomal hsp104 mutants that affect residues considered structurally or functionally relevant to Hsp104 remodeling activity, yet most remain to be examined for their significance to [PSI⁺] in the same genetic background. Many of these hsp104 mutants were affected both in thermotolerance and [PSI⁺] propagation. However, nine mutants were impaired exclusively for [PSI⁺], while two mutants were impaired exclusively for thermotolerance. Mutations exclusively affecting [PSI⁺] are clustered around the lateral channel of the Hsp104 hexamer. These findings suggest that Hsp104 possesses shared as well as distinct remodeling activities for stress-induced protein aggregates and [PSI⁺] prion aggregates and that the lateral channel plays a role specific to [PSI⁺] prion propagation.     

Isolation and characterisation of transposon-induced mutants of Erwinia carotovora subsp. atroseptica exhibiting reduced virulence

Summary The blackleg pathogen Erwinia carotovora subsp. atroseptica (Eca) causes an economically important disease of potatoes. We selected a genetically amenable Eca strain for the genetic analysis of virulence. Tn5 mutagenesis was used to generate nine mutants which exhibited reduced virulence (Rvi^-) of strain SCRI1043. Following physiological characterisation, mutants were divided into three classes: (1) auxotrophs; (2) extracellular enzyme mutants; and (3) a growth rate mutant. The isolation of these Rvi^- mutants has allowed us to consider some factors that affect Eca virulence.     

Isolation and characterization of coaggregation-defective (Cog−) mutants ofStreptococcus gordonii DL1 (Challis)

Streptococcus gordonii DL1 (Challis) bears coaggregation-mediating surface adhesins which recognize galactoside-containing surface polysaccharides onStreptococcus oralis 34,Streptococcus oralis C104, andStreptococcus SM PK509. Fifty-nine spontaneously-occurring coaggregation-defective (Cog^–) mutants ofS. gordonii DL1 unable to coaggregate with partner streptococci were isolated. Six representative Cog^– mutants were characterized by their coaggregation properties with fourActinomyces naeslundii strains (T14V, PK947, PK606, PK984),Veillonella atypica PK1910, andPropionibacterium acnes PK93. The six representative Cog^– mutants showed altered coaggregation with their streptococcal partners,A. naeslundii PK947, andP. acnes PK93. Based on the coaggregation phenotypes of these mutants, a model for the lactose-inhibitable coaggregation betweenS. gordonii DL1 and its partner bacteria is proposed. The potential use of these mutants in studies of oral biofilms is discussed.     

Bilirubin oxidase‐like proteins from Podospora anserina: promising thermostable enzymes for application in transformation of plant biomass

Plant biomass degradation by fungi is a critical step for production of biofuels, and laccases are common ligninolytic enzymes envisioned for ligninolysis. Bilirubin oxidases (BODs)‐like are related to laccases, but their roles during lignocellulose degradation have not yet been fully investigated. The two BODs of the ascomycete fungus Podospora anserina were characterized by targeted gene deletions. Enzymatic assay revealed that the bod1^Δ and bod2^Δ mutants lost partly a thermostable laccase activity. A triple mutant inactivated for bod1, bod2 and mco, a previously investigated multicopper oxidase gene distantly related to laccases, had no thermostable laccase activity. The pattern of fruiting body production in the bod1^Δbod2^Δ double mutant was changed. The bod1^Δ and bod2^Δ mutants were reduced in their ability to grow on ligneous and cellulosic materials. Furthermore, bod1^Δ and bod2^Δ mutants were defective towards resistance to phenolic substrates and H₂O₂, which may also impact lignocellulose breakdown. Double and triple mutants were more affected than single mutants, evidencing redundancy of function among BODs and mco. Overall, the data show that bod1, bod2 and mco code for non‐canonical thermostable laccases that participate in the degradation of lignocellulose. Thanks to their thermal stability, these enzymes may be more promising candidate for biotechnological application than canonical laccases.     

Supersensitive double mutants in yeast

Summary Double mutants containing the radiosensitive alleles uxsl (UVR^-EXR^-) and either uvsl-2 or uvsl 9-2 (both UVR^-EXR⁺) have been constructed. We find that these double mutants are extremely sensitive to UV: their LD₃₇ doses are 0.3–0.5 ergs/mm² as compared to 16–40 ergs/mm² for the radiosensitive parental strains carrying only a single mutant gene and 456 ergs/mm² for wild-type.