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At least 91 records · Page 5Linked to original sources
PubMed1975

The role of DNA polymerase I in genetic recombination and viability of Escherichia coli.

The rate of formation of high-molecular-weight daughter DNA in the conditionally lethal double mutant polA12 uvrE502, incubated at nonpermissive temperature, was slower than that in the single polA12 mutant. There exist at least two pathways determining viability of Escherichia coli cells: one of them is dependent on polA+ and recB+ genes, while another is polA+ and recB+ genes, while another is polA recB independent but requires the uvrE+ gene and can be blocked by exonuclease I. The RecF but not the RecBC pathway of genetic recombination was found to be absolutely dependent on the polymerizing activity of DNA polymerase I. The involvement of DNA polymerase I in genetic recombination in the recB- C- sbsB strain and viability in the uvrE- or recB- strains suggest the existence of the common steps required for the accomplishing of the RecF pathway of recombination and for viability of E. coli.

Cell Survival↗
PubMed1976

Isolation and characterization of lambdadargECBH transducing phages and heteroduplex analysis of the argECBH cluster.

Transducing lambda bacteriophages have been isolated which carry the divergently transcribed argECBH operon of E. coli K12 and various portions of the adjacent ppc and bfe chromosomal regions. They were recovered from lysates prepared by the procedure of Schrenk and Weisberg using a Ppc+ Arg+ Bfe+ strain carrying a deletion of the usual attachment site of lambda. Heteroduplex DNA mapping of these lumbdadarg and of the phi 80 darg isolated by B. Konrad indicates that the two kinds of phages carry the arg cluster in opposite orientations, a situation favorable for the isolation of argECBH DNA. A physical map of the ppc argECBH bfe region including 2 unusual attachment sites of lambda has been constructed. The localization of the end points of certain arg deletions provides a useful reference framework for the currently pursued mapping of mutations affecting the control of divergent transcription and for the location of restriction enzyme cleavage sites in the arg region.

Arginine↗
PubMed1976

Isolation of rec- mutants from an F-prime merodiploid strain of Escherichia coli K-12.

This paper describes a method of screening mutagenised populations of an E. coli galA/galB F- prime merodiploid for mutants defective in recombination. The method relies on scoring colonies on Eosin-Methylene Blue agar that have fewer than normal numbers of Gal+ papillae. With a suitable choice of gal- mutations most of the papillae arise by recombination and some of those colonies with less than normal numbers prove to be defective in some aspect of recombination or DNA repair. In addition to strains carrying mutations that can be ascribed to known loci, several novel mutant phenotypes were identified.

Coliphages↗
PubMed1979

The structure of the phi 80d3 ilv+ Su+7 transducing phage and the origin of its Su+7 tRNA-gene containing fragment.

The Bam HI, XhoI, and EcoRI sites of the transducing phage phi 80d3Su+7ilv+ are located. The 1.2 x 10(6) MD EcoRI fragment which, when cloned, contains tRNAAsp and expresses the mutant tRNATry gene, Su+7, and which also relaxes control of stable RNA synthesis is found immediately adjacent to the rrnC region. Its tRNA genes, tRNAAsp and tRNATry, are transcribed in the same direction as the ribosomal RNA genes, though no mature rRNA subsequences are on the fragment. This fragment also exists as such in another F-prime factor derived from the same Hfr host, and therefore presumably also in the Hfr chromosome itself. It is composed of about half ordinary chromosomal and half F DNA sequences, the latter from the gamma-delta region of F. The advantages of a novel mapping method used are discussed.

Chromosome Mapping↗
PubMed1979

Genetic organization of the Salmonella typhimurium ilv gene cluster.

A number of Salmonella typhimurium ilv::Tn10 insertion strains were used to analyze the Salmonella ilv gene cluster. Tn10 generated ilv deletion mutants were employed in mapping experiments to conclusively define the gene order as ilvG-E-D-A-C. Examination of ilv enzyme levels confirms that the direction of transcription of ilvGEDA is from ilvG to ilvA. The major control locus, designated ilvO, is located before ilvG forming an ilvOGEDA transcriptional unit that is multivalently repressed by isoleucine, valine and leucine. Two internal promoters, one before ilvE and anonother before ilvD, are identified and are shown to provide repressed levels of the ilvE, D and A gene products. Possible regulation of transcription from these promoters in response to isoleucine limitation is discussed in terms of attenuation.

Chromosome Mapping↗
PubMed1980

Interactions between the F conjugal transfer system and CloDF13::Tna plasmids.

It was confirmed that all the F transfer genes required for the formation of stable mating pairs, including traN and traG, are essential for transfer of the two small multicopy plasmids ColE1 and cloDF13, whereas the traM, traI and traZ genes that are required for F conjugal DNA metabolism, are not. Differences between ColE1 and CloDF13 were that the F traD gene was needed for transfer of ColE1 but not of CloDF13, and that R100-1 efficiently transferred CloDF13 but not ColE1. A copy number mutant of CloDF13 inhibited F transfer and reduced plaque formation by the F-specific RNA phage f2, but not by Q beta or by the single-strand DNA phage f1. This phenotype suggests that the inhibition system (FinC) acts on traD, mutations in which give a similar phenotype. Hybridisation experiments with lambda tra phage DNA showed that transcription of traD was not reduced, and FinC probably inhibits function of the traD product rather than its synthesis. FinC-insensitive Flac mutants were isolated and characterised. One was shown to have an uppromoter mutation resulting in increased transcription of traJ and hence of the traY leads to Z operon including traD: the raised level of the traD product presumably then counteracted FinC inhibition.

Bacteriophage lambda↗
PubMed1991

A new oxygen-regulated operon in Escherichia coli comprises the genes for a putative third cytochrome oxidase and for pH 2.5 acid phosphatase (appA)

The Escherichia coli acid phosphatase gene appA is expressed in response to oxygen deprivation and is positively controlled by the product of appR (katF) which encodes a putative new sigma transcription-initiation factor. However, transcription of appA from its nearest promoter (P1) did not account for total pH 2.5 acid phosphatase expression and was not subject to regulation. The cloned region upstream of appA was extended and analyzed by insertions of transposon TnphoA and by fusions with lacZ. It contains two new genes, appC and appB, which both encode extracytoplasmic proteins. appC and appB are expressed from a promoter (P2) lying just upstream of appC. Both genes are regulated by oxygen, as is appA, and by appR gene product exactly as previously shown for appA. Analysis of the nucleotide sequence and of the origins of transcription have confirmed that the P2-appC-appB- (ORFX)-P1-appA region is organized on the chromosome as an operon transcribed clockwise from P2 and that P1 is a minor promoter for appA alone. Genes appC and appB encode proteins of Mr 58,133 and 42,377, respectively, which have the characteristics of integral membrane proteins. The deduced amino acid sequences of appC and appB show 60% and 57% homology, respectively, with subunits I and II of the E. coli cytochrome d oxidase (encoded by genes cydA and cydB). The notion that the AppC and AppB proteins constitute a new cytochrome oxidase or a new oxygen-detoxifying system is supported by the observation of enhanced sensitivity to oxygen of mutants lacking all three genes, cyo (cytochrome o oxidase), cyd (cytochrome d oxidase) and appB, compared to that of cyo cyd double mutants.

Acid Phosphatase↗