Recalibrated linkage map of Escherichia coli K-12

Genetic circularity of the Pseudomonas aeruginosa PAO chromosome

Genetic circularity of the Pseudomonas aeruginosa PAO chromosome was demonstrated by a series of two- and three-factor crosses and double-selection experiments with Cma plasmids FP2, FP5, FP110, and R68.45. A range of additional markers, including catabolic markers, were located on the chromosome map. Plasmid FP2, known to have a major origin of chromosome transfer (0 min) was shown to have at least one other minor origin from which it can transfer the chromosome in the direction opposite to that found for the major origin.

Escherichia coli K-12 clones that overproduce dam methylase are hypermutable

A strain of Escherichia coli K-12 that overproduces dam methylase 50-fold was found to be hypermutable, and mutations which resulted in loss of excess methylase activity restored mutation frequencies to wild-type levels. These results are consistent with involvement of this deoxyribonucleic acid methylase in mismatch correction.

Regulation of hexuronate system genes in Escherichia coli K-12: multiple regulation of the uxu operon by exuR and uxuR gene products

New regulatory mutants of Escherichia coli K-1 carrying alterations of the uxuR gene were isolated and characterized. In the presence of superrepressed or derepressed uxuR mutations, mannonic hydrolyase (uxuA) and oxidoreductase relationship analyses suggested that the uxuR gene product acted as a repressor in the control of uxuA-uxuB operon expression. uxuR mutations were localized near min 97, and the following gene order was established: (argH)-uxuR-uxuB-uxuA-(thr). Properties of exuR (point and deletion) mutants showed that both exuR and uxuR regulatory gene products were involved in the control of the uxuA uxuB operon. Analysis of exuR uxuR double-derepressed mutants suggested that exuR and uxuR repressors act cooperatively to repress the uxu operon.

Organization and structure of an E. coli tRNA operon containing seven tRNA genes

The structure and organization on the Escherichia coli chromosome of the gene cluster coding for two methionine tRNAs (tRNAmMet), four glutamine tRNAs (two tRNA1Gln and two tRNA2Gln), and a previously unidentified tRNA (called tRNAx) have been studied by restriction enzyme analysis and DNA sequencing, utilizing a specialized transducing bacteriophage (lambda psu degrees 2) carrying the supB-supE region. From the sequence analysis, the previously unidentified tRNA has been shown to have an anticodon sequence (5'-UAG-3') corresponding to a leucine codon. The organization of this tRNA gene cluster on the E. coli chromosome is tRNAmMet-9 base pairs-tRNAx-23 base pairs-tRNA1Gln-34 base pairs-tRNA1Gln-15 base pairs-tRNAmMet-47 base pairs-tRNA2Gln-37 base pairs-tRNA2Gln. The duplicated genes coding for tRNAmMet, tRNA,Gln, and tRNA2Gln have identical sequences, which are the same as the sequences determined previously with tRNA molecules. These tRNA sequences are preceded by a single promoter region where a "Pribnow box" sequence is present seven base pairs upstream from the transcription start site. The spacer regions separating the seven tRNA sequences are different from each other both in size and in nucleotide sequence. The possible implication of these sequences for precursor processing is discussed. A restriction fragment that has been originally identified in lambda psu degrees 2 DNA and shown to contain the seven tRNA genes has been detected in the E. coli chromosome, thereby suggesting that this tRNA gene cluster is present in the bacterial genome with the same organization as in the transducing phage genome.

Analysis of the physiological effects of the antibiotic streptozotocin on Escherichia coli K 12 and other sensitive bacteria

The antibiotic streptozotocin under a variety of growth conditions rapidly and irreversibly inactivates the capacity to divide or to form colonies of a series of sensitive bacteria, containing the phosphoenolpyruvate-dependent sugar-phosphotransferase system. Cells can be sensitized towards the drug by pregrowth in N-acetyl-glucosamine and can be protected by adding this amino-glucoside to the medium. Starvation for energy, especially for phosphoenolpyruvate, or prevention of the induction of a transport system involved in streptozotocin uptake will protect the cells, while a block in protein synthesis does not. The killed cells neither lyse, nor are they transformed into spheroplasts. At first, the capacity of such "dead" cells to respire, to swim actively or to keep the cytoplasmic membrane impermeable for small molecules remains intact. Their capacity for over-all RNA and protein synthesis, and for carbohydrate and amino acid uptake by facilitated diffusion or active transport is not affected. However, they loose rapidly their ability to take up carbohydrates by the phosphoenolpyruvate dependent process of group translocation or to synthesize inducible enzymes, e.g. the enzyme beta-galactosidase. These inhibitory effects apparently are caused by the accumulation of phosphorylated, toxic derivatives of the antibiotic and eventually lead to a pronounced bacteriostasis. Killing of the cells seems to be caused by a direct effect of the strongly mutagenic drug on replicating DNA.

Genetic and biochemical properties of Escherichia coli mutants with defects in serine chemotaxis

In Escherichia coli, taxis to certain chemoeffectors is mediated through an intrinsic membrane protein called methyl-accepting chemotaxis protein I (MCP I), which is the product of the tsr gene. Mutants were selected that are defective in taxis toward all MCP I-mediated attractants (alpha-aminoisobutyrate, L-alanine, glycine, and L-serine) but are normal to MCP I-mediated repellents and to chemoeffectors mediated by other MCPs. The mutants could be divided into two classes based on their ability to respond to various concentrations of L-serine. Two MCP I-mediated L-serine systems appear to function in the wild type: one of high and one of lower affinity. The mutations responsible for the serine taxis defects map at about 99 min on the E. coli chromosome and are not complemented by episomes carrying mutations in the tsr gene; this suggests that they are defective in tsr function. Low concentrations of L-[14C]serine specifically bound to wild-type membranes with a Km of 5 microM; in contrast, there was greatly decreased binding to vesicles prepared from the new mutants or from the tsr mutant AW518. Binding of labeled serine to wild-type vesicles was inhibited by MCP I-mediated attractants, but not by MCP II-mediated attractants. The data suggest that MCP I may function as the L-serine chemoreceptor in E. coli.

Organization of unc gene cluster of Escherichia coli coding for proton-translocating ATPase of oxidative phosphorylation

The proton-translocating ATPase (F1-F0) of oxidative phosphorylation (ATP phosphohydrolase, EC 3.6.1.3) is coded for by a set of structural genes comprising the unc operon in Escherichia coli. We have analyzed several new transducing phages and plasmids carrying various lengths of the DNA segments of the unc operon by complementation assay using 14 new unc- mutants and representatives of previously described strains which were made available to us. Transducing phages carrying parts of the unc gene cluster were isolated: lambda uncA-9 and lambda glmS phages converted only some of the unc- mutants to the Unc+, as determined by complementation assays. A new hybrid plasmid (pMCR533) carrying part of the unc operon was constructed by inserting the HindIII fragment of lambda asn-5 DNA (a phage carrying the entire unc operon) into the unique HindIII site of pBR322. This plasmid transformed eight unc- strains to Unc+, including uncB402 and uncA401, but did not complement uncD11 or four other strains. Two minichromosomes which carry the E. coli replication origin were also tested: plasmid pNH05 transformed the uncB402 but not the uncA401 strain to Unc+, whereas plasmid pMCF1 transformed none of the mutants tested. Analysis of the DNAs from these transducing phages and plasmids with restriction endonucleases suggested that all of the structural genes for the F1-F0 complex are localized within a DNA segment of approximately 4.5 megadaltons containing two EcoRI sites. The approximate locations of the unc- mutations were mapped on this DNA segment.

The variation in frequency with which markers are transduced by phage P1 is primarily a result of discrimination during recombination

The efficiency of recovery of P1 transductants is marker dependent and normally varies over a 25-fold range. UV irradiation of either transducing lysates for recipient cells results in a selective stimulation of the transduction of markers which are normally transduced poorly. As a result the range in frequency of transduction is reduced to about 3-fold and resembles the gene frequency distribution expected in the donor cells. We conclude that P1 transducing lysates are likely to contain a random sample of donor DNA but that the recombination system of the recipient cell exhibits a preference for the DNA of some regions over that of others. Damage to DNA presumably overrides this specificity.

Amber mutation affecting the length of Escherichia coli cells

An amber mutation in a newly found gene (wee) of Escherichia coli has been isolated from strain OV-2, which harbors a temperature-sensitive suppressor. At 42 degrees C cells of the mutant, OV-25, increased in mass and deoxyribonucleic acid content and divided at normal rates, compared with the wild type under the same growth conditions. Total cell length increased under the restrictive conditions, although at a slightly lower rate. Values of mean cell length and cell volume, contrary to what would be expected from the increment in the rate of increase in particles, mass, and deoxyribonucleic acid, became at 42 degrees C smaller than those found in the wild type. A parallel increase in protein content per length and cell density and a loss of viability were found to occur after four generations at the restrictive temperature. The behavior of strain OV-25 in the absence of the wee gene product could be interpreted in terms of either a faulty regulation of the elongation processes or their abnormal coordination with the cell cycle. The genetic location of the wee gene has been found to be at 83.5 min on the E. coli genetic map.

Analysis of ultraviolet light-induced suppressor mutations in the strain of Escherichia coli K-12 AB1157: an implication for molecular mechanisms of UV mutagenesis

Genetic analysis of histidine independent (His+) revertants induced by ultraviolet light in the his-4 E. coli strain AB1157 was carried out: 93% carried ochre (UAA) suppressor mutations and 17% carried back mutations to his+ or (intragenic?) suppressors not detectably separable from his-4. Using the specialized transducing lambda psu 2int- phage, which carries supE-supB, it was determined that 87% of the ochre suppressors mapped in the supE-supB region. We were able to deduce that 56% of these affected tRNA1Gln by a CAA leads to TAA change in the tRNA gene while 31% affected tRNA2Gln by TAG- leads to TAA change. Although we were unable to deduce the base substitution of the remaining 13%, the results indicate that most of the suppressor mutations are caused by G:C to A:T transition. These results suggest that the high incidence of supE-supB region suppressor mutation in E. coli by UV would be a reflection of the general feature of UV mutagenesis; i.e. preferential induction of G:C to A:T transition in repairing nonpairing DNA lesions. AI 05371

Interaction between aminoglycoside uptake and ribosomal resistance mutations

Mutants resistant to the 2-deoxystreptamine aminoglycosides hygromycin B and gentamicin were analyzed biochemically and genetically. In hygromycin B-resistant strains, ribosomal alterations were not detectable by electrophoretic or genetic experiments. Rather, as was demonstrated for one strain in detail, resistance to this drug seems to be the consequence of several mutations, each impairing drug accumulation, namely of a deletion of a gene close to the proC marker which potentiates the effect of a second mutation in the unc gene cluster. Three mutants resistant to gentamicin which were previously demonstrated to harbor an altered ribosomal protein, L6, were shown in addition to contain unc. Both the unc and the ribosomal mutation greatly impair the drug accumulation ability of the mutants. Further evidence for the direct effect of ribosomal mutations on the uptake of aminoglycosides was obtained with strains that possess ribosomes with increased affinity for dihydrostreptomycin. Dihydrostreptomycin transport by these cells is greatly stimulated; thus, the hypersensitivity of these mutants is caused by increased binding affinity for dihydrostreptomycin and its secondary effect on the uptake process. Experiments were also performed on the biochemical basis of the third phase of aminoglycoside transport (acceleration phase). The condition for its onset is that ribosomes are active in protein synthesis irrespective of whether the proteins synthesized are functional. This, and the failure to observe the synthesis of new proteins upon the addition of aminoglycosides, do not support the view of autoinduction of a cognate or related transport system.

High frequency mobilization of the chromosome of Escherichia coli by a mutant of plasmid RP4 temperature-sensitive for maintenance

Two mutants of plasmid RP4 temperature-sensitive for maintenance were isolated and one of them (pTH 10) was extensively studied. Cells carrying pTH10 showed temperature-sensitive drug resistance from which we isolated a number of temperature-independent derivatives. Almost all of them were Hfrs donating chromosomal genes to recipient bidirectionally from different points of origin. The Hfrs may be formed in two steps: (1) the transposon (Tn 1) carried by pTH 10 translocates into the host chromosome, and (2) pTH 10 is integrated in the host chromosome by reciprocal recombination between the TN 1 s, one situated on pTH 10 and another on the host chromosome. That temperature-independent drug resistance selects for this type of derivative, was supported by the following observations: (1) Hfrs thus obtained were usually unstable and segregated at high frequency 'revertants' showing temperature-sensitive drug resistance when they were cultivated at 30 degrees C. (2) The 'revertants' cured of pTH 10 were still ampicillin resistant, indicating existence of Tn 1 inserted in the host chromosome. (3) Tn 1 insertions found in these derivatives mapped in the vicinity of points of origin of the original Hfrs. (4) When new Hfrs were constructed by: (a) transduction with Plkc on Tn 1 insertions found in derivatives of Hfrs, (b) introduction of pTH 10 into the transductants,and (c) isolation of clones of temperature-independent drug resistance from such pTH 10 carrying stains, they had similar characteristics to the original Hfrs from which Tn 1 insertions were derived. Possibilities for genetic manupulation using pTH 10 in a wide range of Gram-negative bacteria are discussed.

Amber mutations in the structural gene for RNA polymerase sigma factor of Escherichia coli

Amber mutants of Escherichia coli K-12 affected in the structural gene (rpoD) for the sigma subunit of RNA polymerase have been obtained from a strain harboring a temperature-sensitive amber suppressor (supF-Ts6) which is active only at low temperatures. These mutants grow normally at low temperature (30 degrees C) but do not grow at high temperature (42 degrees C) due to the inability to synthesize sigma factor. In one mutant studied in detail (rpoD40), the rate of sigma-factor synthesis at 30 degrees C is about half that of the wild type and is decreased to 10%-15% within 1 h of incubation at 42 degrees C. The synthesis of core polymerase subunits or bulk protein is virtually unaffected at least for 2 h. The defect of the mutant in sigma synthesis and growth at high temperature can be suppressed by any of the amber suppressors tested (supD. supE or supF). RNA-polymerase holoenzymes prepared from the mutant cells carrying each of the suppressors (grown at 42 degrees C) exhibit different thermostabilities attributable to alterations in the sigma factor. The reduced sigma synthesis in the mutant is accompanied by the synthesis of polypeptide tentatively identified as 'amber fragment'. These results as well as the genetic mapping data indicate that the amber mutation (rpoD40) resides within the structural gene for the sigma factor and directly affects sigma synthesis upon inactivation of the suppressor at high temperature.

Structural instability of IncP-1 plasmids in Pseudomonas aeruginosa PAT involves interaction with plasmid pVS1

The structural instability exhibited by IncP-1 plasmids in Pseudomonas aeruginosa strain PAT was shown to be Rec+ dependent and involved interaction with the resident plasmid pVS1. Structural instability resulted from deletion of plasmid deoxyribonucleic acid at a frequency of ca. 10(-2)/cell per generation. Deletants could be stabilized by transduction into P. aeruginosa strain PAO, but in strain PAT deletants had only a transient existence, as continued deletion led eventually to the loss of the entire plasmid. The patterns of markers lost in PAT were used to demonstrate a marker order for R68 similar to that published elsewhere for RP4 (Barth and Grinter, J. Mol. Biol. 113:455-474, 1977), except that only one Tra region was found. R68 also exhibited Rec+-dependent structural instability in PAO(pVS1) derivatives but, unlike the case in PAT, instability was not accompanied by chromosome mobilization. We isolated deletants of pVS1 which were unable to promote structural instability.

Identification of new genes in a cell envelope-cell division gene cluster of Escherichia coli: cell envelope gene murG

We report the identification, cloning, and mapping of a new cell envelope gene, murG. This lies in a group of five genes of similar phenotype (in the order murE murF murG murC ddl) all concerned with peptidoglycan biosynthesis. This group is in a larger cluster of at least 10 genes, all of which are involved in some way with cell envelope growth.

Isolation and mapping of a mutation in Escherichia coli with altered levels of ribonuclease H

A mutant of Escherichia coli with altered levels of ribonuclease (RNase) H was isolated after mutagenesis with ethyl methane sulfonate. A procedure for assaying RNase H in partially purified extracts was used to screen approximately 1,500 colonies for variations in RNase H activity. Confirmation of a lower level of RNase H in the mutant was accomplished by analysis of RNase H in sodium dodecyl sulfate-polyacrylamide gels. By Hfr, F', and P1 transduction mapping, the genetic locus responsible for the lower levels of RNase H was located at 5.1 min on the E. coli chromosome. This mutation (rnh) represents a new locus on the E. coli chromosome. The only phenotypic characteristic of this mutation which has been observed to date is the lower level of RNase H (30% of parental values).

Acetaldehyde coenzyme A dehydrogenase of Escherichia coli

Mutants of Escherichia coli (adh) in which alcohol dehydrogenase is derepressed under aerobic conditions were also found to overproduce acetaldehyde coenzyme a dehydrogenase. However, acetaldehyde coenzyme A dehydrogenase was induced by ethanol or acetaldehyde and subject to strong catabolite repression, whereas alcohol dehydrogenase was little affected by these conditions. Mutants no longer able to use ethanol as carbon source were isolated from an adh strain. Some of these mutants were revertants at the adh locus and no longer produced either alcohol dehydrogenase or acetaldehyde coenzyme A dehydrogenase. Others, designated acd, were found to lack only acetaldehyde coenzyme A dehydrogenase. The acd mutation was located at min 62 of the E. coli genetic map, the gene order being thyA-lysA-acd-serA-fda. Isolation of Tn10 insertions cotransducible with acd greatly simplified the mapping procedure.

Identification of new genes in a cell envelope-cell division gene cluster of Escherichia coli: cell division gene ftsQ

We report the identification, cloning, and mapping of a new cell division gene, ftsQ. This gene formed part of a cluster of three division genes (in the order ftsQ ftsA ftsZ) which itself formed part of a larger cluster of at least 10 genes, all of which were involved in some step in cell division, cell envelope synthesis, or both. The ftsQAZ group was transcribed from at least two independent promoters.

Pleiotropic mutations rendering Escherichia coli K-12 resistant to bacteriophage TP1

tpo mutations, located at 74 min on the genetic map, rendered Escherichia coli K-12 resistant to TP1, a phage which can use either the OmpF protein or the LamB protein as its receptor. tpo mutants synthesized decreased amounts of OmpF and LamB proteins but increased amounts of the OmpC product, another outer membrane protein. The effect of the tpo mutations in lam B gene expression was transcriptional. It is one facet of the following effect on the maltose regulon: strong decreases in the syntheses of the LamB protein and the periplasmic MalE protein occurred when the regulon was uninduced; a lesser decrease occurred in the syntheses of the LamB protein the MalE protein, and the cytoplasmic MalQ protein (amylomaltase) when the regulon was induced. The tpo mutants were found to be phenotypically identical to the perA mutant recently described by Wanner et al. (J. Bacteriol. 140:229--239, 1979) and to some of the ompB mutants described by Verhoef et al. (Mol. Gen. Genet. 169:137--146, 1979). Mapping and complementation analysis suggested that these three types of mutations belong to the same cistron. Our results bring to at least four the number of clearly distinct phenotypes which can result from mutations at, or close to, ompB, a locus which appears increasingly complex.

recA gene product is responsible for inhibition of deoxyribonucleic acid synthesis after ultraviolet irradiation

Deoxyribonucleic acid synthesis after ultraviolet irradiation was studied in wild-type, uvrA, recB, recA recB, and recA Escherichia coli strains. Inhibition of deoxyribonucleic acid synthesis, which occurs almost immediately after exposing the cells to ultraviolet radiation, depends on the functional gene recA.

Expression of Klebsiella his and nif genes in Serratia marcescens, Erwinia herbicola and Proteus mirabilis

Plasmid pRD1, an R plasmid of the P incompatibility group which carries his and nif genes from Klebsiella pneumoniae in addition to drug resistance markers derived from RP4, was transferred to His- mutants of Serratia marcescens, Erwinia herbicola and Proteus mirabilis. His+ transconjugants were obtained at low but different frequencies according to recipient genus. Transconjugants all acquired the drug resistance, and were Nif+ in S. marcescens and E. herbicola, having acetylene-reducing activities of the same order of magnitude as the parent K. pneumoniae and fixing 15N2. No evidence for nif expression in P. mirabilis transconjugants was obtained though the nif genes were present.

Genetic characterization of a filament-forming, lipoprotein-deficient mutant of Escherichia coli

The fam-715 allele of Escherichia coli ST715, previously described as a temperature-sensitive filament former with reduced levels of lipoprotein at the nonpermissive temperature (S. V. Torti and J. T. Park, Nature [London] 263: 323--326, 1976), was mapped at 74 min. This mutation appears to be amber. It is recessive and can be complemented by F' plasmids carrying the wild-type allele or by an F' plasmid carrying an amber suppressor. Isotopic labeling experiments as well as map position differentiate the fam-715 allele from lipoprotein structural gene mutations.

purF-lac fusion and direction of purF transcription in Escherichia coli

The purF locus codes for the first enzyme, glutamine phosphoribosylpyrophosphate amidotransferase, of the purine biosynthetic pathway. A strain of Escherichia coli K-12 was isolated in which the lac structural genes were fused to the control region of the purF locus. This purF-lac fusion was shown to respond to purine-specific regulatory signals. A plaque-forming lambda transducing phage bearing this purF-lac fusion was isolated. This phage was used to genetically determine the direction of transcription for the pufF locus by two independent means. Results from both methods agreed that the direction of transcription of the purF locus was clockwise on the standard Escherichia coli K-12 genetic map.

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.

Map location of the ssd mutation in Escherichia coli K-12

A pleiotropic mutation at the ssd locus was mapped at 86 min near rha. A mutation at the ssd locus resulted in elevated L-serine deaminase activity, inability to grow with succinate as the carbon source, and inability to grow anaerobic conditions.

Genetic fine structure of the pyrE region containing the genes for ribosomal proteins L28 and L33 in Escherichia coli

Temperature-sensitive mutants harbouring alterations in ribosomal proteins L28 and L33 have been isolated and used in mapping the genes coding for the two proteins. It was found that they mapped very close to each other and near pyrE at 80.7 min on the E. coli genetic map. The genes affected by the mutations have been concluded to be the structural genes for proteins L28 (rpmB) and L33 (rpmG) by constructing merodiploids heterozygous for pyrE and for the two ribosomal proteins. Various transduction studies with P1kc phages indicate the gene order in this region to be (rpmB, rpmG)-pyrE-spoT-gltC.

Physical mapping and expression of hybrid plasmids carrying chromosomal beta-lactamase genes of Escherichia coli K-12

Hybrid plasmids carrying the ampC gene of Escherichia coli K-12 that codes for the chromosomal beta-lactamase were physically studied. The ampC gene was mapped to a deoxyribonucleic acid segment encompassing 1,370 base pairs. The mapping was facilitated by the isolation of a plasmid carrying an insertion of the transposable element gamma delta (gamma delta) close to ampC. The ampA1 mutation, which increases the expression of ampC by a factor of about 20, was localized to a 370-base pair segment of the 1,370-base pair deoxyribonucleic acid segment that contains the ampC gene. Using a minicell protein labeling system, it was seen that plasmids carrying either ampA+, ampC, or ampA1 and ampC coded for a 36,000-dalton protein which comigrated with purified chromosomal beta-lactamase. In cells carrying plasmids that bore the ampA1 allele, the production of this protein was greater. In addition, a protein with a slightly higher molecular weight (38,000) was expressed by both ampA+ ampC and ampA1 ampC plasmids in this protein labeling system. This protein might represent a precursor form of chromosomal beta-lactamasee. From E. coli K-12 strains carrying the ampA1 allele, second-step mutants were isolated that hyperproduced chromosomal beta-lactamase. By reciprocal recombination, plasmid derivatives were isolated that carried these mutations. Two second-step regulatory mutations mapped within the same 370-base pair region as ampA1. This piece of deoxyribonucleic acid therefore contains ampA, a control sequence region for ampC.

Localization of the plasmid (pKM101) gene(s) involved in recA+lexA+-dependent mutagenesis

Twenty Tn5 insertion mutants of the drug resistance plasmid pKM101 have been isolated that are unable to enhance mutagenesis with ultraviolet (UV) irradiation or methyl methanesulfonate. By restriction mapping, the Tn5 insertion in each of these pKM101 mutants was shown to be within a 1.9 kb region of the plasmid genome. We have termed this segment of the pKM101 map the muc (mutagenesis: UV and chemical) gene(s). Characterization of these mutants indicated that any Tn5 insertion within the muc gene(s) abolished the ability of pKM101 to: (a) enhance spontaneous, UV and chemical mutagenesis, (b) increase host survival following UV-irradiation, (c) increase the survival of UV-irradiated phage plated on irradiated or unirradiated cells, and (d) suppress the repair and mutagenesis deficiencies of a umuC- mutant. Possible models to explain the role of the pKM101 muc gene(s) in mutagenesis and repair are discussed.

Kinetics and regulation of cell-free alkaline phosphatase synthesis

Regulation of alkaline phosphatase (EC 3.1.3.1) synthesis in a cell-free system from Escherichia coli has been observed. Synthesis from transducing phage deoxyribonucleic acid templates carrying phoA+ occurred in S30 fractions from wild-type or alkaline phosphatase-constitutive mutants. It did not occur in S30) fractions from alkaline phosphatase-negative mutants (phoB). The hybrid gene phoA-lacZ was also subject to phoB control, implying that phoA transcription is regulated. The yield of active alkaline phosphatase per phoA+ gene copy from cell-free synthesis was similar to that of beta-galactosidase. Alkaline phosphatase activity took longer to appear than beta-galactosidase activity. Synthesis of alkaline phosphatase subunits was not delayed, suggesting that a minimum number of subunits are synthesized before formation of active alkaline phosphatase occurs.

Synthesis and function of ribonucleic acid polymerase and ribosomes in Escherichia coli B/r after a nutritional shift-up

The syntheses of stable ribosomal ribonucleic acid (RNA) and transfer RNA in bacteria depend on the concentration and activity of RNA polymerase and on the fraction of active RNA polymerase synthesizing stable RNA. These parameters were measured in Escherichia coli B/r after a nutritional shift-up from succinate-minimal to glucose-amino acids medium and were found to change in complex patterns during a 1- to 2-h period after the shift-up before reaching a final steady-state level characteristic for the postshift growth medium. The combined effect of these changes was an immediate, one-step increase in the exponential rate of stable RNA synthesis and thus of ribosome synthesis. This suggests that the distribution of transcribing RNA polymerase over ribosomal and nonribosomal genes and the polymerase activity are continuously adjusted during postshift growth to some growth-limiting reaction whose rate increases exponentially. It is proposed that this reaction is the production of amino-acylated transfer RNA and that is exponentially increasing rate results in part from a gradually increasing concentration of aminoacyl transfer RNA synthetases after a shift-up. This idea was tested and is supported by a computer simulation of a nutritional shift-up.

Regulation of Escherichia coli K-12 hexuronate system genes: exu regulon

Two types of Escherichia coli K-12 regulatory mutants, partially or totally negative for the induction of the five catabolic enzymes (uronic isomerase, uxaC; altronate oxidized nicotinamide adenine dinucleotide: uxaB; mannonate hydrolyase, uxuA) and the transport system (exuT) of the hexuronate-inducible pathway, were isolated and analyzed enzymatically. Hexuronate-catabolizing revertants of the negative mutants showed a constitutive synthesis for some or all of these enzymes. Negative and constitutive mutations were localized in the same genetic locus, called exuR, and the following order for the markers situated between the min 65 and 68 was determined: argG--exuR--exuT--uxaC--uxaA--tolC. The enzymatic characterization of the pleiotropic negative and constitutive mutants of the exuR gene suggests that the exuR regulatory gene product exerts a specific and total control on the three exuT, uszB, and uxaC-uxaA operons of the galacturonate pathway and a partial control on the uxuA-uxuB operon of the glucuronate pathway. The analysis of diploid strains conatining both the wild type and a negative or constitutive allele of the exuR gene, as well as the analysis of thermosensitive mutants of the exuR gene, was in agreement with a negative regulatory mechanism for the control of the hexuronate system.

Restriction map of the Escherichia coli malA region and identification of the malT product

A series of plaque-forming lambda h80 transducing phages carrying various portions of the malA region were isolated. A 5,800-base pair HindIII-EcoRI DNA fragment from one of these phages was cloned into pBR322 and shown to contain malT, which is the positive regulator gene of the maltose regulon, and most of malP, the structural gene for maltodextrin phosphorylase. A restriction map of the HindIII-EcoRI fragment was established, and it was correlated with the genetic map of the malA region (i) by mapping deletions which had been generated in vitro on the plasmid and (ii) by locating on the restriction map a DNA insertion of known genetic position. A 600-base pair HincII-HaeII segment was shown to contain all or part of the promoters for malT and malP, which are known to be transcribed in opposite directions. Strains carrying gene malT on a plasmid synthesized a 94,000-dalton polypeptide which was not produced by identical strains carrying similar plasmids in which malT was partially deleted. Estimates of the size of the malT gene support the conclusion that the 94,000-dalton polypeptide is the malT product.

Specificity in the formation of delta tra F-prime plasmids

Twenty-three independent delta tra F-prime plasmids from three different Escherichia coli K-12 sublines were isolated from Hfr strains whose points of origin coincided with the IS3 element alpha 3 beta 3 or alpha 4 beta 4 in the lac-purE region of the E. coli chromosome. Electrophoretic analysis of plasmid deoxyribonucleic acid digested with EcoRI and hybridization analysis of plasmid deoxyribonucleic acid digested with BglII revealed that at least 14 of these plasmids were formed by processes involving specific bacterial and F loci. Two of the specific bacterial loci involved in delta tra F-prime formation were located at approximately 3.3 and 11.7 min on the E. coli chromosomal map. Two of the delta tra F-prime plasmids contained bacterial deoxyribonucleic acid with circularization endpoints that mapped very near the termini of the IS2 element that is normally located between lac and proC.

ColV plasmid-mediated, colicin V-independent iron uptake system of invasive strains of Escherichia coli

Evidence is presented that ColV plasmid-mediated iron uptake, an important component of the virulence of invasive strains of Escherichia coli, is independent of colicin V synthesis and activity. A mutant of E. coli K-12 deficient in the biosynthesis of enterochelin (strain AN1937) was unable to grow on minimal agar containing the chelating agent alpha,alpha'-dipyridyl unless it was harboring the plasmid ColV-K30 (strain LG1315). Acquisition of the active plasmid-specified iron sequestering system was accompanied by marked enhancement of pathogenicity in experimental infections of mice. Mutants of strain LG1315 were isolated that were defective in iron uptake due to plasmid mutations. They were unchanged with respect to colicin production, but were significantly less virulent than the parent strain. Conversely, mutants isolated as defective in colicin V synthesis were normal for the plasmid-coded iron uptake mechanism and showed the same lethality for infected mice as did strain LG1315. Furthermore, mutations in strain AN1937 which render it resistant or tolerant to the bactericidal action of colicin V did not influence the uptake of iron into plasmid-carrying strains. Cross-feeding tests involving plasmid mutants defective in iron uptake identified two plasmid-specified components of the system, an extracellular iron-chelating compound and a nondiffusible product allowing transport of iron across the bacterial cell membrane.

Use of gene cloning to determine polarity of an operon: genes carAB of Escherichia coli

A gene-cloning approach was used to determine the transcription polarity of the carbamoylphosphate operon (carAB) of Escherichia coli. In agreement with the accompanying paper (J. Bacteriol. 143:914-920, 1980), our results lead to the conclusion that carA is the proximal gene of the carAB operon.

Runaway replication of plasmid R1 is not caused by loss of replication inhibitor activity of gene cop

The replication control functions of a mutant of plasmid R1 that replicates without control at temperatures above 35 degrees C have been analyzed. Although the mutations have not been mapped precisely, the data indicate that the gene (cop) previously identified on the wild-type plasmid (S. Molin and K. Nordström, J. Bacteriol. 141:111-120, 1980) as being responsible for expressing a trans-acting replication inhibitor, as well as for incompatibility of plasmid R1, is not affected in this mutant. Thus, the conditional lack of replication control observed in this plasmid mutant presumably is not caused by the loss of inhibitor activity of the cop gene.

Spontaneous emergence of an Hfr strain with a cit plasmid from natural isolates of citrate-positive Escherichia coli bovine origin

From citrate-utilizing (Cit+) Escherichia coli strain C53 of bovine origin, strains C53A and C53B were obtained. Upon mating with recA+ but not with recA mutant recipients of K-12, C53A produced chromosomal recombinants at quite high frequencies, leading to the following conclusions: (i) C53A is an Hfr strain; (ii) the site of integration of the Cit plasmid (IncH1) is between metA (89 min) and ara (1 min); (iii) the direction of chromosome transfer is clockwise; and (iv) the plasmid-associated determinants are transferred as the terminal markers. A transductant of a dnaA(Ts) strain, CRT46, which acquired Cit determinants from a recombinant, SG13, was also an Hfr strain similar to SG13, and thermoresistant due to suppressive integration. On the other hand, unstable C53B did not produce recombinants, but the frequency of RecA-independent transfer of the Cit plasmid was high, indicating that the Cit plasmid (IncH1) exists autonomously in C53B. Attempts to isolate an Hfr strain from C53B failed.

Polyprenyl p-hydroxybenzoate carboxylase in flagellation of Salmonella typhimurium

Flagellation of Salmonella typhimurium was found to require a functional pathway for ubiquinone biosynthesis as well as growth in the presence of appropriate carboxylic acids. Induction of flagellation by carboxylic acids was shown to induce incorporation of p-hydroxybenzoic acid into polyprenylphenol. Constitutive flagellation was found to correlate with constitutive incorporation of p-hydroxybenzoic acid into polyprenylphenol. A novel pathway for polyprenyl p-hydroxybenzoic acid decarboxylation to polyprenylphenol was implicated in flagellation of S. typhimurium.

Locations of the opp and supX genes of Salmonella typhimurium and Escherichia coli

The chromosomal locations of the supX and opp loci of Salmonella typhimurium LT2 and Escherichia coli K-12 were identified and found to result in the same gene sequence in both species, namely, pyrF-cysB-supX-trpPOLEDCBA-tonB(chr)-opp. These results differ from a previously reported location of the opp gene on the E. coli chromosome. Evidence indicates that the opp gene lies between chr(tonB) and galU in S. typhimurium.

Isolation and characterization of lambda transducing phages for the E. coli genes ksgA and pdxA

Lambda phages carrying the Escherichia coli genes ksgA and pdxA were isolated from secondary site lysogens in araB. 1) The phage genomes were characterized by genetic complementation tests, restriction endonuclease digestion and electron microscopy. 2) A 6.3 kilobasepair (kb) EcoRI restriction fragment carrying both ksgA and pdxA was cloned in a lambda vector; this fragment has proven useful in further characterization of the ksgA gene (Andrésson and Davies, 1980a, b). The ksgA and pdxA genes are about 14 and 12-13 kb, respectively, counterclockwise of the arabinose operon and 1.5 and 2.5-3.5 kb clockwise of folA.

The ral gene of phage lambda. I. Identification of a non-essential gene that modulates restriction and modification in E. coli

Host controlled restriction in Escherichia coli can be relieved by pre-infecting restricting cells with modified lambda helper phages. This process, in which intact unmodified phage genomes are allowed to escape restriction attack, is mediated by a newly identified lambda function called ral. The ral gene has been located by deletion mapping between cIII and N. Efficient expression of the ral gene requires the product of the regulator gene N. Polyacrylamide gel analysis of the lambda proteins specified by the cIII-N region failed to reveal the product of the ral gene, but demonstrated that protein Ea10 is encoded by a gene located immediately to the left of ral. From these results the map order cIII-Ea10-ral-TL1-N was deduced. Ral specifically alleviates restriction in E. coli K and E. coli B, but does not affect restriction systems EcoRI, EcoRII and EcoP1. In addition, ral enhances the modification activity of the EcoK and EcoB restriction enzymes: we observed that efficient modification of progeny phages obtained by propagating unmodified lambda phages in r-m+ hosts, is dependent upon the presence of ral. We thus conclude that the ral gene product acts by modulating the restriction and modification activities of the type I restriction systems in E. coli, and the possible mechanisms will be discussed.