Rapid mapping of conditional and auxotrophic mutations in Escherichia coli K-12

Another gene affecting sexual expression of Escherichia coli

We have examined the relationship between two chromosomal mutations of Escherichia coli K-12, fexA (0 min) and fexB (85 min), in regulating expression of the F sex factor. Together, fexA and fexB exert a pleiotropic effect on the expression of the F tra genes. F pilus synthesis, conjugal donor activity, and surface exclusion activity are all inhibited in the fexA fexB mutant. Either fex mutation alone is cryptic.

Genetic mapping of mutation in Escherichia coli leading to a temperature-sensitive RNase D

In order to determine the metabolic role of RNase D in Escherichia coli, we have attempted to isolate strains deficient in this enzyme. One strain containing a temperature-sensitive RNase D was found among a heavily mutagenized stock of strain temperature-sensitive for growth. Genetic mapping of the mutation responsible for the altered RNAse D enabled us to define the rnd locus, at 39.5-40.0 min on the E. coli map, which apparently specifies the RNase D structural gene. Using a Tn10 insertion near the rnd locus, we constructed isogenic strains containing RNase D and Rnase II mutations, alone or in combination. Although the original mutant isolate displayed temperature-sensitive growth. no growth phenotype was associated with the rnd mutation in wild type background, possibly because a substantial amount of RNase D remained in cells grown at 45 degrees C. However, elucidation of the map position of the rnd locus should prove useful for the isolation of other mutant strains with lower levels of RNase D.

Export of a protein into the outer membrane of Escherichia coli K12. Stable incorporation of the OmpA protein requires less than 193 amino-terminal amino-acid residues

The cloned ompA gene encoding the major outer membrane protein OmpA of Escherichia coli has been shortened in vitro by exonuclease digestion from the end corresponding to the CO2H terminus of the protein. Nine derivatives were identified which still possessed substantial parts of the ompA gene and one was constructed which had suffered a small deletion early in the gene. Gene fragments encoding NH2-terminal OmpA sequences of 45, 133, 193, and 227 residues of the 325 amino acids of OmpA were examined in detail at the DNA level and for OmpA protein fragments synthesized. The latter two fragments were incorporated into the outer membrane and all known functions of the OmpA protein were expressed whereas the fragment with 133 OmpA-specific residues was not stably incorporated into this membrane. In all cases where OmpA functions were observed, an OmpA-specific polypeptide of Mr 24 000 was found in cell envelopes, regardless of the size of the residual ompA sequences and of the fused coding sequences in the vector DNA. Pulse-label experiments revealed larger initial translation products, most of which were degraded to the protein of Mr 24000. The 133-residue OmpA fragment was also detected but proved to be entirely unstable. It is argued that the OmpA protein consists of two domains and that the NH2-terminal moiety from residues 1 to about 180 represents the membrane domain of the polypeptide. Therefore, the loss of about 50, possibly less, CO2H-terminal residues from this domain suffices to interfere with stable incorporation into the outer membrane.

Enhanced recombination between F42lac and lambda plac5: dependence on F42lac fertility functions

F42lac recombination with lambda plac5 is normally twentyfold to fiftyfold higher than recombination between lambda plac5 and a chromosomal lac gene. The presence of an fi+ R1 plasmid in the same cell as F42lac dramatically reduces this enhanced recombination level while the fi- R1drd19 plasmid has little effect. When F42lac traJ90 is tested in a sup+ strain, it shows a sharp reduction in recombination with lambda plac5 that can be largely reversed by the presence of a supF mutation that partially suppresses the traJ90 nonsense mutation. It is concluded that the enhanced recombination between F42lac and lambda plac5 is largely dependent on the constitutive expression of F42lac fertility functions.

Conversion of potentially lethal damage to lethal damage in Escherichia coli inhibited by caffeine

In E. coli cells with potentially lethal damage to their DNA are starved of amino acids they rapidly lose viability (Koukalová and Kuhrová 1980). This phenomenon is called secondary lethality (SL). In the course of secondary lethality there is a decrease in the molecular weight of DNA to a value on average three times lower (DNA fragmentation, and part of the DNA is reduced to acid-soluble fractions (DNA degradation). Caffeine inhibits SL, and both these processes of DNA decay, The lowest effective concentration 5 mg/ml, with maximum effect at a concentration of 10 mg/ml. SL is also inhibited by the absence of an energy source. The possible mechanism of SL is discussed on the basis of these results.

Functional cooperation of the dnaE and dnaN gene products in Escherichia coli

A system was designed to isolate second-site intergenic suppressors of a thermosensitive mutation of the dnaE gene of Escherichia coli. The dnaE gene codes for the alpha subunit of DNA polymerase III [McHenry, C. S. & Crow, W. (1979) J. Biol. Chem. 254, 1748-1753]. One such suppressor, named sueA77, was finely mapped and found to be located at 82 min on the E. coli chromosome, between dnaA and recF, and within the dnaN gene [Sakakibara, Y. & Mizukami, T. (1980) Mol. Gen. Genet. 178, 541-553]. The dnaN gene codes for the beta subunit of DNA polymerase III holoenzyme [Burgers, P. M. J., Kornberg, A. & Sakakibara, Y. (1981) Proc. Natl. Acad. Sci. USA 78, 5391-5395]. The sueA77 mutation was trans-dominant over its wild-type allele, and it suppressed different thermosensitive mutations of dnaE with different maximal permissive temperature. These properties were interpreted as providing genetic evidence for interaction of the dnaE and dnaN gene products in E. coli.

Inducibility of a gene product required for UV and chemical mutagenesis in Escherichia coli

The product of the umuC gene is required for UV and chemical mutagenesis in Escherichia coli. By the use of the Mud(Ap, lac) bacteriophage, we have obtained an operon fusion of the lac structural genes to the promoter/regulatory region of the umuC gene. The strain containing the umuC::Mud(Ap, lac) fusion was identified on the basis of its UV nonmutability. Strains containing this putative null allele of umuC were (i) nonmutable by UV and other agents, (ii) slightly UV sensitive, and (iii) deficient in their ability to carry out Weigle reactivation of UV-irradiation bacteriophage lambda. The UV nonmutability of the strain could be suppressed by a derivative of the mutagenesis-enhancing plasmid pKM101. beta-Galactosidase synthesis in umuC::Mud(Ap, lac) fusion strains was inducible by UV and other DNA-damaging agents. Genetic analysis of the regulation of beta-galactosidase in umuC::Mud(Ap, lac) strains suggests that the lexA protein is the direct repressor of the umuC gene and that a function of the recA protein, probably its protease activity, is required for the removal of the lexA repressor at the time of umuC induction.

The effects of NMR exposure on living organisms. I. A microbial assay

Various bacterial strains have been exposed to a homogeneous magnetic field of 1 Tesla and to the conditions found in an NMR imaging experiment of the type used in a recent abdominal scan (Mansfield et al., 1978). No mutagenic or lethal effects were observed. The activity of the bacterial enzyme beta-galactosidase was also found to be independent of the applied magnetic field.

Isolation and genetic characterization of Escherichia coli mutants defective in propionate metabolism

Escherichia coli mutants defective in propionate metabolism (Prp-) were isolated after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. Prp- mutants demonstrate a phenotypic inability to grow on odd-chain-length fatty acids. The new genetic locus for the Prp- phenotype maps at approximately 98 min on the E. coli chromosome.

Specialized transduction with lambda plac5: dependence on recA and on configuration of lac and att lambda

The construction of lambda plac5 transducing phages carrying various lacZ alleles is described. Genetically disabled (N- N- P-) lambda plac transducing the phages were used to study the dependence of specialized transduction on host RecA function and on the location of the lacZ gene in the recipient strain. In the absence of site-specific recombination at att lambda, transduction was completely dependent on host RecA function. Regardless of the configuration of att lambda, lambda plac transducing phages recombined at a 20- to 50-fold higher frequency with F42 lac than with a lac gene located in the cellular chromosome. Deletion mutants of lacZ in the recipient strain were used to show that the probability of lac recombination resulting from lambda plac infection is apparently proportional to the amount of homology between the parental lacZ genes.

Formation of Escherichia coli Hfr strains by integrative suppression with the P group plasmid RP1

Hfr strains of Escherichia coli were obtained by integrative suppression of a dnaA(Ts) mutation by the Inc P-1 plasmid RP1 without prior creation of an unnatural homology between the plasmid and the E. coli chromosome. Unmodified RP1 mobilized the polarized transfer of the chromosome in a counterclock-wise direction from a distinct origin between 81 min (pyrE) and 82 min (dnaA) with pyrE as a leading marker. Inheritance of RP1-Hfr chromosomal and antibiotic resistance genes was due to recombination with the recipient chromosome, as shown by the need for a functional recA system. The acquisition of temperature resistance and donor ability was accompanied by the disappearance of free plasmid when the selection pressure for integration was maintained (growth at 41 degrees C); the loss of temperature resistance and donor ability was accompanied by the reappearance of autonomous RP1 when the selection pressure was removed (growth at 30 degrees C).

Genetic analysis of gene 1.2 of bacteriophage T7: isolation of a mutant of Escherichia coli unable to support the growth of T7 gene 1.2 mutants

The product of gene 1.2 of bacteriophage T7 is not required for the growth of T7 in wild-type Escherichia coli since deletion mutants lacking the entire gene 1.2 grow normally (Studier et al., J. Mol. Biol. 135:917-937, 1979). By using a T7 strain lacking gene 1.2, we have isolated a mutant of E. coli that was unable to support the growth of both point and deletion mutants defective in gene 1.2. The mutation, optA1, was located at approximately 3.6 min on the E. coli linkage map in the interval between dapD and tonA; optA1 was 92% cotransducible with dapD. By using the optA1 mutant, we have isolated six gene 1.2 point mutants of T7, all of which mapped between positions 15 and 16 on the T7 genetic map. These mutations have also been characterized by DNA sequence analysis, E. coli optA1 cells infected with T7 gene 1.2 mutants were defective in T7 DNA replication; early RNA and protein synthesis proceeded normally. The defect in T7 DNA replication is manifested by a premature cessation of DNA synthesis and degradation of the newly synthesized DNA. The defect was not observed in E. coli opt+ cells infected with T7 gene 1.2 mutants or in E. coli optA1 cells infected with wild-type T7 phage.

Suppressor mutations that restore export of a protein with a defective signal sequence

A selection procedure is described that should allow the genetic identification of cellular components involved in the process of protein localization in Escherichia coli. This procedure makes use of mutations that alter the signal sequence of the lambda receptor protein (product of the lamB gene), and prevent export of this protein to its normal outer membrane location. Several suppressor mutations have been identified that restore export of the mutant lambda receptor protein. Mapping experiments show that the suppressor phenotype is the result of mutations in any of at least three different chromosomal loci. One class of suppressor mutations, the class containing the largest number of independent isolates, maps in the major ribosomal gene cluster, suggesting that the suppressor phenotype is the consequence of an altered ribosomal protein. This class of suppressors phenotypically suppresses all known export-defective mutations, internal to the signal sequence region of the lamB gene. These results suggest that ribosomes play an important role in the export of lambda receptor to the outer membrane.

Hyper-recombination in uvrD mutants of Escherichia coli K-12

A mutant strain of E. coli which was isolated initially because of its strong hyper-recombination phenotype was shown to carry a lesion in uvrD. The presence of this mutation, designated uvrD210, increased the frequency of recombination between chromosomal duplications in F-prime repliconant cells and reduced linkage between closely linked markers in crosses with Hfr donors. A comparable hyper-rec phenotype was demonstrated in strains carrying other alleles of uvrD previously referred to as mutU4, uvr502 and recL152. The recombination activity of a uvrD210 strain was abolished by mutation of recA but the mutator activity associated with this allele proved to be independent of recA. It is suggested that uvrD mutations reduce the fidelity of DNA replication and that the accumulation of lesions in the newly synthesized strand provides additional sites for initiating recombination.

Genetic analysis of Escherichia coli K-12 chromosomal mutants defective in expression of F-plasmid functions: identification of genes cpxA and cpxB

Two temperature-sensitive, chromosomal mutants of Escherichia coli were selected for their inability to express deoxyribonucleic acid donor activity and other activities associated with the conjugative plasmid F. These mutants were also auxotrophic for isoleucine and valine at 41 degrees C. Each mutant strain contained two altered genes: cpxA, located at 88 min on the E. coli K-12 genetic map, and cpxB, located at 41 min. Mutations in both genes were required for maximal expression of mutant phenotypes. The parent strain of mutants KN401 and KN312 already contained the cpxB mutation that is present in both mutants (cpxB1). This mutation by itself was cryptic. The cpxA mutations represent different mutant alleles since they are of independent origin. A cpxA mutation by itself significantly affected the expression of plasmid functions and growth at 41 degrees C in the absence of isoleucine and valine, but strains containing both a cpxA and cpxB mutation were more severely affected. Along with the observation that both cpxA mutations were revertable, the temperature sensitivity of cpxA cpxB+ cells suggests that both cpxA alleles contain point mutations that do not completely destroy the activity of the cpxA gene product.

Impaired incision of ultraviolet-irradiated deoxyribonucleic acid in uvrC mutants of Escherichia coli

The production of single-strand breaks in the deoxyribonucleic acid of irradiated uvrC mutants of Escherichia coli K-12 was studied both in vivo and in vitro. In vivo, uvrC mutants displayed a slow accumulation of breaks after irradiation, and in this respect appeared different from uvrA mutants, in which very few breaks could be detected. The breakage observed in uvrC mutants differed from that observed in wild-type strains in both the slow rate of break accumulation and the very limited dose response. The behavior of the uvrC lig-7(Ts) double mutant was shown not to be consistent with the suggestion of ligase reversal as the explanation for the lower rate and limited dose response of break formation observed in ultraviolet-irradiated uvrC mutants in vivo. Rather, there appeared to be a real defect in incision. In toluene-treated cells, we studied the effect of the ligase inhibitor nicotinamide mononucleotide on strand incision. Whereas uvrC mutants displayed more strand breakage in the presence of this inhibitor, the same amount of breakage was seen in uvrA mutants, and as such the breakage could be judged as not due to the main excision repair pathway. Experiments using a cell-free system comprising the partially purified uvr+ gene products demonstrated clearly that there is a requirement for the uvrC+ gene product for strand incision. We suggest that in vivo in the absence of the uvrC+ gene product, a partial analog of this protein may allow some abnormal incision.

Selection of Escherichia coli K-12 chromosomal mutants that prevent expression of F-plasmid functions

Chromosomal mutants of Escherichia coli deficient in the expression of F-plasmid functions were selected by mutagenizing F- cells, introducing an F' plasmid into the mutagenized cells by conjugation, and identifying transconjugants resistant to the donor-specific bacteriophage Q beta by a simple spray test. All but 1 of 25 mutants were defective in an extracellular stage of Q beta infection, suggesting that they fail to elaborate F-pili. At least six of these were also deficient as deoxyribonucleic acid donors. More than half of the mutants appear to be altered in peviously undetected chromosomal genes required for the expression of F-related cellular functions.

Role of the host cell in bacteriophage T4 development. II. Characterization of host mutants that have pleiotropic effects on T4 growth

Mutant host-defective Escherichi coli that fail to propagate bacteriophage T4 and have a pleiotropic effect on T4 development have been isolated and characterized. In phage-infected mutant cells, specific early phage proteins are absent or reduced in amount, phage DNA synthesis is depressed by about 50%, specific structural phage proteins, including some tail and collar components, are deficient or missing, and host-cell lysis is delayed and slow. Almost all phage that can overcome the host block carry mutantions that map in functionally undefined 'nonessential' regions of the T4 genome, most near gene 39. The mutant host strains are temperature sensitive for growth and show simultaneous reversion of the ts phenotype and the inability to propagate T4+. The host mutations are cotransduced with ilv (83 min) and may lie in the gene for transcription termination factor rho.

Loss of Hfr DNA from Escherichia coli merozygotes during inhibition of conjugation by nalidixic acid

The effect of nalidixic acid on conjugal recombination was studied in matings with recipient strains carryingrecA200, a mutation which confers a thermosensitive Rec−phenotype. Addition of nalidixic acid to Hfr Nals× F−NalRrecA200matings at low temperature (35 °C) caused a sharp 10- to 20-fold decline in the yield of recombinants if plating on selective agar was delayed. Two separate processes were identified as being responsible for this decline. Those merozygotes in which the transferred DNA was free of the donor cell lost the ability to form recombinants through inactivation of this DNA, an effect which could be prevented by using exonuclease deficient (recB sbcB) recipients or by prior growth of exonuclease proficient recipients in medium containing 0·25 M sodium chloride. No more than 50% of the observed loss of recombinants could be attributed to this effect. The remaining merozygotes lost their ability for recombinant formation provided mating pairs, and presumably the displaced donor DNA strand, remained intact. This process was thought to involve withdrawal of transferred DNA (DeHaan & Gross, 1962) and was studied in isolation in matings withrecA+, orrecA200 recB sbcBrecipients. A mechanism involving re-annealing of the displaced Hfr DNA to the donor molecule as a result of nalidixic inhibition of gyrase activity in the donor causing relaxation of DNA supercoils is proposed to account for this withdrawal event.

Isolation and preliminary characterization of single amino acid substitution mutants of aspartate carbamoyltransferase

In order to isolate functional Escherichia coli aspartate carbamoyltransferase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC2.1.3.2) with single amino acid replacements, a series of pyrB nonsense mutants has been isolated. These nonsense mutants were induced by 2-aminopurine mutagenesis and selected by a combination of antibiotic treatments, direct enzyme assays, and suppressibility tests. Suppression of the pyrB nonsense mutation with various suppressors, which insert different amino acids, has resulted in the formation of a series of mutant aspartate carbamoyltransferases, each differing in one amino acid from the wild-type enzyme. After partial purification, kinetic studies revealed that some of the mutant enzymes had altered homotropic and heterotropic interactions. The mutants that had a tyrosine insert showed the most pronounced changes, followed by those with a serine insert. The mutants having a glutamine insert, howevr, were indistinguishable from the wild-type enzyme, supporting the conclusion that, because of the specificity of the mutagen, the glutamine insert had regenerated the wild-type enzyme.

Regulation of fatty acid degradation in Escherichia coli: isolation and characterization of strains bearing insertion and temperature-sensitive mutations in gene fadR

Transposon Tn10 was used to mutagenize the fadR gene in Escherichia coli. Mutants bearing fadR:Tn10 insertion mutations were found to (i) utilize the noninducing fatty acid decanoate as sole carbon source, (ii) beta-oxidize fatty acids at constitutive rates, and (iii) contain constitutive levels of the five key beta-oxidative enzymes. These characteristics were identical to those observed in spontaneous fadR mutants. The constitutive phenotype presented by the fadR:Tn10 mutants was shown to be genetically linked to the associated transposon-encoded drug resistance. These results suggest that the fadR gene product exerts negative control over the fatty acid degradative regulon. The fadR gene of E. coli has been mapped through the use of transposon-mediated fadR insertion mutations. The fadR locus is at 25.5 min on the revised map and cotransduces with purB, hemA, and trp. Three-factor conjugational and transductional crosses indicate that the order of loci in this region of the chromosome is purB-fadR-hemA-trp. Spontaneous fadR mutants were found to map at the same location. Strains that exhibit alterations in the control of the fad regulon in response to changes in temperature were also isolated and characterized. These fadR(Ts) mutants were constitutive for the fad enzymes at elevated temperatures and inducible for these activities at low temperatures. The fadR(Ts) mutations also map at the fadR locus. These results strongly suggest that the fadR gene product is a repressor protein.

Cloning and restriction mapping of the trmA gene coding for transfer ribonucleic acid (5-methyluridine)-methyltransferase in Escherichia coli K-12

A hybrid plasmid from the Clarke and Carbon collection has been isolated. This plasmid carries the trmA gene of E. coli, which is necessary for the formation of 5-methyluridine (m5U,ribothymidine) present in all transfer ribonucleic acid (tRNA) chains of the organism so far sequenced. A restriction map of the argCBH-trmA regions is presented. By using cloning in vitro, the trmA gene was located on a 2.9-kilobase pair deoxyribonucleic acid (DNA) fragment. These results and comparison with lambda dargECBH transducing phages established the gene order: argECBH trmA bfe in the 88-min region of the E. coli chromosomal map. Plasmids carrying this 2.9-kilobase pair DNA fragment overproduce the enzyme tRNA(m5U)methyltransferase (EC 2.1.1.35) 20 to 40 times. When this 2.9-kilobase pair chromosomal DNA fragment was expressed in a minicell system, a polypeptide of a molecular weight of 42,000 was synthesized. This polypeptide was tentatively identified as the tRNA(m5U)methyltransferase. These results support the earlier suggestion that the trmA gene is the structural gene for the tRNA(m5U)methyltransferase.

Integration of bacteriophage Mu at host chromosomal replication forks during lytic development

The target site for bacteriophage Mu integration in a lytic cycle of infection was investigated. DNA synthesis in five Hfr strains of Escherichia coli K-12 was synchronized by amino acid starvation and was allowed to proceed for 0, 8, or 15 min before infection. The Hfr cells were then infected with Mu and were subsequently mated with nonimmune F- recipient cells. Mating was interrupted mechanically at 5-min intervals and samples were assayed for infective centers. Conjugal transfer of Mu was delayed in Hfr strains that have transfer origins 15 map units or more from the E. coli replication origin, and the delays increased as the distance between an Hfr point of origin and the replication origin increased. When a gene A mutant of Mu was used for the infection, no infective centers were generated. Infection with a gene B mutant resulted in infective center formation only after long periods of mating. These data are most consistent with a model in which infecting Mu DNA or its progeny integrate at host chromosomal replication forks.

Serine sensitivity of Escherichia coli K 12: partial characterization of a serine resistnat mutant that is extremely sensitive to 2-ketobutyrate

E. coli wild type bacteria display sensitivity towards serine. A selection medium is described which allows selection of serine resistant mutants. One such mutant is described which presents pleiotropic alterations: it exhibits a thermosensitive growth pattern, alteration in the metabolism of the pppGpp and ppGpp nucleotides, cAMP intracellular level alteration, extreme sensitivity to 2-ketobutyric acid and a defect in the phosphotransferases permeation system. A conjecture explaining these apparently unrelated defects supposes that serine metabolism interferes via phosphoenol pyruvate with a cytoplasmic control of membrane activity (the mutant would be defective in the coupling between membrane and the protein responsible for its cytoplasmic control) and that 2-ketobutyrate is an effector of this activity.

Genetic mapping and some characterization of the rnpA49 mutation of Escherichia coli that affects the RNA-processing enzyme ribonuclease P

A mutant defective in the enzyme RNase P was isolated by P. SCHEDL and P. PRIMAKOFF (1973). The mutation rnpA49 found in this strain, which confers temperature sensitivity on carrier strains, was mapped by conjugation and transduction experiments and located around minute 82 of the E. coli map, with the suggested order rnpA bglB phoS rbsP ilv. As expected, the rnpA49 mutation is recessive. Even though this mutation is conditional, it is manifested at temperatures at which the carrier strains can grow.

Escherichia coli regulatory mutation affecting lysine transport and lysine decarboxylase

A spontaneous thiosine-resistant mutant of Escherichia coli was shown to have the following characteristics: lowered initial rate of lysine uptake and lowered plateau level of accumulation of exogenous lysine by both the lysine-specific and the general basic amino acid transport systems; altered repressibility of these two lysine transport systems; a derepressed level of lysine decarboxylase; normal growth rate; parental levels of lysyl-transfer ribonucleic acid synthetase and the inducible and constitutive arginine and ornithine decarboxylases. Both the mutant (lysP) and its parent (lysP+) feed a lysine auxotroph when they are plated in proximity on solid medium. However, the feeding response was observable after 1 day less of incubation when the mutant was the feeding strain. Despite the derepressed level of lysine decarboxylase in exponential cultures of the mutant extracts of these cultures had no detectable cadaverine pool. Conjugation experiments established the following gene order: gyrA (formerly nalA) lysP metG his. All thiosine-resistant recombinants assayed showed reduced lysine transport. In many of these recombinants the derepression of lysine decarboxylase was not expressed.

Escherichia coli mutants with altered control of alcohol dehydrogenase and nitrate reductase

Mutants of Escherichia coli which overproduce alcohol dehydrogenase were obtained by selection for the ability to use ethanol as an acetate source in a strain auxotrophic for acetate. A mutant having a 20-fold overproduction of alcohol dehydrogenase was able to use ethanol only to fulfill its acetate requirement, whereas two mutants with a 60-fold overproduction were able to use ethanol as a sole carbon source. The latter two mutants produced only 25% of the wild-type level of nitrate reductase, when grown under anaerobic conditions. Alcohol dehydrogenase production was largely unaffected by catabolite repression but was repressed by nitrate under both aerobic and anaerobic conditions. The genetic locus responsible for alcohol dehydrogenase overproduction was located at min 27 on the E. coli genetic map; the gene order, as determined by transduction, was trp tonB adh chlC hemA. The possible relationship of alcohol dehydrogenase to anaerobic redox systems such as formate-nitrate reductase is discussed.

Genetic analysis of Escherichia coli mutants defective in adenylate kinase and sn-glycerol 3-phosphate acyltransferase

Complementation analysis with independently isolated plA and adk (adenylate kinase) mutants of Escherichia coli showed that all the mutants belong to the same complementation group. The results suggest that the adk (plsA) locus is the structural gene for adenylate kinase.

Mutant single-strand binding protein of Escherichia coli: genetic and physiological characterization

A mutation in the Escherichia coli gene for single-strand binding protein results in temperature-sensitive deoxyribonucleic acid replication (R. R. Meyer, J. Glassberg, and A. Kornberg, Proc. Natl. Acad. Sci. U.S.A. 76:1702-1705, 1979). The mutant (ssb-1) is also more sensitive to ultraviolet irradiation and about one-fifth as active in recombination. Single-strand binding protein is thus implicated in repair and recombination as well as in replication. The mutation in ssb is located between uvrA and melA at 90.8 min on the genetic map. The ssb gene appears to be allelic with lexC, a gene with a proposed role in regulating inducible deoxyribonucleic acid repair.

Isolation and characterization of Escherichia coli K-12 mutants unable to induce the adaptive response to simple alkylating agents

When Esherichia coli cells are exposed to a low level of simple alkylating agents, they induce the adaptive response which renders them more resistant to the killing and the mutagenic effects of the same or other alkylating agents. This paper describes the isolation of one strain that was deficient in mutagenic adaptation and five that were deficient in both mutagenic and killing adaptation, confirming previous suggestions that killing and mutagenic adaptation are, at least to some extent, separable. These six strains have been called Ada mutants. They were more sensitive to the killing and mutagenic effects of N-methy-N'-nitro-N-nitrosoguanidine (MNNG) than the unadapted Ada+ parent. Thus, the adaptation pathway is responsible for circumventing some alkylation-induced damage even in cells that are preinduced. The increase in mutation frequency seen in Ada cells treated with MNNG was the same whether the cells were lexA+ or lexA, showing that the extra mutations found in Ada- strains do not depend upon the SOS pathway. Ada strains accumulated more O6-methyl guanine lesions than the Ada+ parent on prolonged exposure to MNNG, and this supports the idea that O6-methyl guanine is the most important lesion for MNNG-induced mutagenesis. The ada mutations have been shown to map in the 47 to 53-min region of the E. coli chromosome.

Properties of Escherichia coli mutants altered in calcium/proton antiport activity

Mutants sensitive to growth inhibition by CaCl2 were found to have alterations in calcium uptake in everted membrane vesicles. These mutations map at different loci on the Escherichia coli chromosomes. A mutation at the calA locus results in vesicles which have two- to threefold higher levels of uptake activity than vesicles from wild-type cells. The calA mutation is phenotypically expressed as increased sensitivity to CaCl2 in a strain also harboring a mutation in the corA locus, which is involved in Mg2+ transport. The calA locus maps very close to purA and cycA at about min 97. The calB mutation results both in sensitivity to CaCl2 at pH 5.6 and in vesicles with diminished calcium transport capability. The CalB phenotype is also expressed only in a corA genetic background; the calB locus appears to map very near, yet separately from, the calA locus. When the cor+ allele is present, calA and calB mutations still result in a defect in calcium transport in vesicles. In addition, both calC and calD mutations result in vesicles with impaired calcium transport activity. calC is cotransducible with kdp and nagA, whereas calD is cotransducible with proC.

Two mutations which affect the barrier function of the Escherichia coli K-12 outer membrane

Two genetically distinct classes of novobiocin-supersensitive mutants were isolated from Escherichia coli K-12. One class, given the phenotypic name NbsA, lies at 10 min on the E. coli chromosome. The order of the genes in this region, based on transductional analyses, is proC NbsA plsA purE. The second, NbsB, lies at 80 min. The order of the genes in this region, based on transduction analyses, is xyl cysE NbsB pyrE. Both classes of mutants show increased sensitivity to hydrophobic drugs but are different: NbsA cells tend to be more sensitive to cationic agents, whereas NbsB cells show the opposite tendency. The sole detectable biochemical alteration in NbsA strain is greater than 90% reduction in the phosphate content of the lipid A region of the lipopolysaccharide. The NbsB mutation results in lipopolysaccharide that contains primarily the stereoisomer D-glycero-D-mannoheptose, rather than L-glycero-D-mannoheptose, and which contains very little of the distal sugars. Since NbsA strains have apparently normal outer membrane proteins and total cellular phospholipids, changes solely in lipopolysaccharide can increase permeability to certain hydrophobic antibiotics. Complementation studies indicate that the NbsA marker is probably allelic with acrA. In addition, the NbsB marker is genetically and phenotypically similar to the rfaD locus of Salmonella typhimurium. For this reason, the phenotypic designations NbsA and NbsB have been changed to the genotypic designations acrA and rfaD, respectively.

Characterization of the dnaA, gyrB and other genes in the dnaA region of the Escherichia coli chromosome on specialized transducing phages lambda tna

Specialized transducing phages lambda tna (tryptophanase) harboring chromosomal DNA and genetic markers from the dnaA region of the Escherichia coli chromosome were isolated. Transductional analysis showed that some of these tnaA transducing phages carry two genes important in DNA replication, namely the dnaA gene (initiation of chromosome replication) and the gyrB gene (subunit B of DNA gyrase), formerly designated couR. The following clockwise order of genetic markers was found: uhp, gyrB, dnaA, rimA, tnaA, bglB. The gene-protein relationship was established by the determination of the gene products encoded on the chromosomal DNA of the different lambda tna. A 54 kD and a 91 kD polypeptide appear to be coded for by the dnaA and gyrB genes, respectively; the 91 kD protein is encoded on a region in which coumermycin sensitivity maps and is with respect to electrophoretic behavior identical to subunit B of DNA gyrase. The 54 kD protein is encoded on the region in which different independently isolated dnaA(Ts) mutations (dnaA5, dnaA46, dnaA167, dnaA203, dnaA204, dnaA205, dnaA211, dnaA508) are located. Additional genes which code for polypeptides with hitherto unknown functions were identified and mapped. The acriflavin sensitivity mutation acrB1 was found to be an allele of the gyrB gene (see "Note Added in Proof").

Isolation and mapping of plasmids containing the Salmonella typhimurium origin of DNA replication

A purified EcoRI restriction endonuclease fragment that determines resistance to kanamycin and is incapable of self-replication was used to select autonomously replicating fragments from an EcoRI digest of a Salmonella typhimurium F' plasmid containing the chromosomal region believed to include the S. typhimurium origin of DNA replication. Both the F factor and S. typhimurium chromosome replication origins were cloned by this procedure. The EcoRI fragmentment containing the S. typhimurium origin of replication is 19.4 kilobase pairs long and includes functional asp+ and uncB+ genes. Restriction endonuclease analysis of deletions obtained from the S. typhimurium origin plasmid indicated that the replication origin (ori region) is contained within a 3.3-kilobase pair region. Comparison with Escherichia coli origin plasmids shows colinearity of gene arrangement on the chromosomes in this region and suggests that some, but not all, regions of the nucleotide sequence in the origin region may be conserved (identical) in these two bacterial species.

Regulation of the biosynthesis of aminoacyl-transfer ribonucleic acid synthetases and of transfer ribonucleic acid in Escherichia coli. V. Mutants with increased levels of valyl-transfer ribonucleic acid synthetase

Spontaneous revertants of a temperature-sensitive Escherichia coli strain harboring a thermolabile valyl-transfer ribonucleic acid (tRNA) synthetase were selected for growth at 40 degrees C. Of these, a large number still contain the thermolabile valyl-tRNA synthetase. Three of these revertants contained an increased level of the thermolabile enzyme. The genetic locus, valX, responsible for the enzyme overproduction, is adjacent to the structural gene, valS, of valyl-tRNA synthetase. Determination (by radioimmunoassay) of the turnover rates of valyl-tRNA synthetase showed that the increased level of valyl-tRNA synthetase is due to new enzyme synthesis rather than decreased rates of protein degradation.

Regulation of the biosynthesis of aminoacyl-transfer ribonucleic acid synthetases and of transfer ribonucleic acid in Escherichia coli. VI. Mutants with increased levels of glutaminyl-transfer ribonucleic acid synthetase and of glutamine transfer ribonucleic acid

Spontaneous revertants of a temperature-sensitive Escherichia coli strain bearing a thermolabile glutaminyl-transfer ribonucleic acid (tRNA) synthetase have been selected for growth at 45 degrees C. Among 10 revertants still containing the thermolabile enzyme, 2 interesting strains were found. One strain has a fivefold elevated level of the thermolabile glutaminyl-tRNA synthetase; the genetic locus, glnR, responsible for this effect maps at min 24, far from glnS, the structural gene of the enzyme. In the other strain the levels of tRNA Gln and several other tRNAs are twice as high as in the parental strain; the locus responsible, glnU, maps at min 59.5 on the E. coli map.

Genetic mapping of a mutation affecting pyridine nucleotide transhydrogenase in Escherichia coli

A mutation, pnt-1, causing loss of pyridine nucleotide transhydrogenase activity in Escherichia coli, was mapped by assaying for the enzyme in extracts of recombinant strains produced by conjugation, F-duction, and P1 transduction. The site of this mutation was near min 35, counterclockwise from man, and it co-transduced 59% with man. The mutation was associated with loss from the cell membrane fraction of energy-independent and adenosine 5'-triphosphate-dependent transhydrogenase activities, but reduced nicotinamide adenine dinucleotide dehydrogenase activity was not affected. Strains were constructed which lack phosphoglucoisomerase (pgi-2) and which carry either pnt+ or pnt-1. Although such strains, when grown on glucose, are expected to produce a large excess of reduced nicotinamide adenine dinucleotide phosphate, the growth rate was not affected by the pnt-1 allele.

Genetic studies of an Escherichia coli K-12 temperature-sensitive mutant defective in membrane protein synthesis

The mutant divE42(Ts) of Escherichia coli K-12, defective in the synthesis of membrane proteins and in the transcription of the lac operon at high temperature, has been further characterized. It was found that a mutation (divE42) located at about min 22 on the E. coli chromosome map is responsible for the Lac- phenotype and temperature-sensitive growth. The mutation could be contransduced with serC, pyrD, or pyrC by phage P1 at a frequency of 4, 16, or 0.5%, respectively, the gene order being serC-pyrD-ompA-sulA-divE-pyrC. Examination of temperature-independent revertants and Pyr+ transductants revealed that all the mutant phenotypes examined (deficiencies in the increase of activities of some membrane enzymes, expression of the lac operon, and synthesis of several other proteins) are due to a single mutation (divE42) which is recessive to the wild-type (divE+) allele. Protein synthesis in the mutant was also analyzed by dodecyl sulfate-polyacrylamide gel electrophoresis. Synthesis of a number of proteins, including membrane proteins, was found to decrease significantly, whereas that of an elongation factor, EF-Tu, increased upon transfer of a log-phase culture to high temperature (42 degrees C). These effects of temperature shift-up on protein synthesis were evident within 5 min under the conditions used.

An Escherichia coli mutant defective in single-strand binding protein is defective in DNA replication

An Escherichia coli mutant, temperature-sensitive for DNA synthesis in vivo and in vitro, is defective in single-strand binding protein (SSB; DNA-binding protein). Conversion of phage G4 single strands to the duplex form is defective in crude enzyme fractions of the mutant and is complemented by pure wild-type SSB. Radioimmunoassays of mutant extracts show normal levels of material crossreacting with anti-SSB antibody. SSB purified to homogeneity from the mutant is active, with lower specific activity, in the reconstituted G4 replication assay at 30 degrees C, but virtually inactive at 42 degrees C. Surprisingly, the mutant protein, like the wild-type protein, survives heating at 100 degrees C. Thus, mutant SSB is structurally heat-resistant but is functionally thermosensitive in vitro and in vivo. Both the in vivo and in vitro defects are tightly linked in transductions by phage P1. The mutation in the binding protein, designated ssb-1, is located between 90 and 91 min on the E. coli genetic map.

Transposon-insertion mutants of Escherichia coli K12 defective in a component common to galactose and ribose chemotaxis

From a collection of 8,000 transposon-insertion mutants of Escherichia coli K12 we identified two mutations, trg-1::Tn5 and trg-2::Tn10, that simultaneously eliminate chemotactic response to ribose and galactose, two attractants recognized by independent receptors. We show that these transposon-insertions confer a Trg phenotype, indicating that this specific pattern of tactic defects is a null phenotype. The two mutation sites are cotransductionally linked to an extend consistent with placement in the same gene. The Trg phenotype of a family of deletion mutants produced by curing trg-2::Tn10 implies that trg is a single gene. Experiments with appropriate F-primes and Hfr's locate the trg locus at approximately 31 min on the linkage map, with a marker order: pyrF-rac-(P.O. 43)-trg-man. We also found one trg mutant whose Trg phenotype was not linked to a transposon-insertion but is probably the result of a mutator activity in the parent strain. Selection of transposon-insertions near, but not in trg allowed demonstration of a very close linkage between the spontaneous trg-3 and the transposon-generated trg's, indicating all three mutations are probably in the same gene. In our manipulations of transposon-insertions we found that Tn5 had a tendency to translocate from its initial site of insertion while Tn10 was relatively stable. The trg-product is probably a chemotactic signal transducer, which interacts directly with two independent receptor proteins and transmits information to the central chemotactic machinery.

Isolation and properties of Escherichia coli K-12 mutants impaired in the utilization of gamma-aminobutyrate

We have isolated mutants of Escherichia coli K-12 CS101B that have lost the ability to utilize gamma-aminobutyrate as a source of nitrogen. One class of mutants, which were not affected in the utilization of other nitrogen sources (proline, arginine, glycine), included many isolates with lesions in gamma-aminobutyrate transport or in its transamination and one mutant completely devoid of succinic semialdehyde dehydrogenase activity and exhibiting low gamma-aminobutyrate transport and transamination. gamma-Aminobutyrate-utilizing revertants of the latter recovered full transport and transamination capacities but remained dehydrogenaseless. Another class of mutants showed pleiotropic defects in nitrogen metabolism. One such mutant was lacking glutamate synthase activity. The genes specifying the synthesis of gamma-aminobutyrate permease, gabP, gamma-aminobutyrate transaminase, gabT, and succinic semialdehyde dehydrogenase, gabD, and the control gene, gabC, that coordinately regulates their expression all form a cluster on the E. coli chromosome, linked to the srl and recA loci (at 57.5 min). The mutations with pleiotropic effects on the metabolism of nitrogenous compounds are not linked to the gab cluster.

Transposon-facilitated recombination in Vibrio cholerae

Improved Vibrio cholerae donors were constructed by introducing the ampicillin transposon, Tn1, into both the conjugative plasmid, P, and the bacterial chromosome to provide "portable regions of homology." The resulting Tfr (Transposon-facilitated recombination) donors transferred genes at high frequency from origins specified by the chromosomally inserted Tn1 copies. Tn1 was transposed into the chromosome from a deleted P::Tn1 vector, which was eliminated from the cells by superinfection with a thermosensitive P::Tn9 (chloramphenicol) mutant plasmid. After eliminating the thermosensitive plasmid, the chromosomally resistant isolates were converted into donors with a P::Tn1 conjugative plasmid. Tfr donors were also obtained by isolating Tn1 insertion mutations in a gene for thymine biosynthesis. Chromosomal sites of Tn1 relative to bacterial genes were determined by measuring gene transfer frequencies and genetic linkage. In one case, linkage of the amp gene to the chromosomal genes that defined its location was demonstrated. Chromosomal transfer by Tfr donors was reversed by isolating P::Tn1 plasmids that contained Tn1 inserted in the opposite orientation.

Glutamyl-gamma-methyl ester acts as a methionine analogue in Escherichia coli: analogue resistant mutants map at the metJ and metK loci

Escherichia coliK-12 mutants resistant to glutamyl-γ-methyl ester were isolated. A mutation leading to resistance of up to 1·4 mg/ml of the methionine analogue maps at min 63 and is 13% cotransducible withserAindicating an alteration in themetKgene. Another mutation leading to resistance to 3 mg/ml of the analogue and cross-resistance to other amino acid analogues maps at min 87. This mutation, which has the phenotype of MetJ−, is shown to be situated between theglpKandmetBgenes and thus indicates a different gene order from the published one.