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Biomedical subjects

A J Clark

Publications and source records attributed to A J Clark.

At least 325 records · Page 18Linked to original sources
PubMed1977

The dependence of postreplication repair on uvrB in a recF mutant of Escherichia coli K-12.

Mutants carrying recF143 or recF144 show wild type levels of host cell reactivation of UV-irradiated lambdavir and wild type rates of excision gap closure in repairing UV damage to their own DNA. The same mutants showed reduced rates of postreplication repair strand joining. When uvrA- recF- or uvrB- recF- strains are tested, postreplication repair strand joining is incomplete or does not occur at fluences above 1 J/m2. We suggest that there may be a UvrAB and a RecF pathway of postreplication repair or that the repair functions controlled or determined by uvrA uvrB and by recF may be similar. An intermediate in postreplication repair may accumulate in the uvr- recF- strain.

DNA Repair↗
PubMed1977

Increase in conjugational transmission frequency of nonconjugative plasmids.

Addition of Eco RI fragment 6 of the Escherichia coli sex factor F to pSC101 increases the frequency of its transmission by RI-19 and ColVB. Transmission frequencies of pSC101 and two pSC101 chimeras are also increased after the putative transposition of drug resistance element Tn3 from RI-19. These increases may result from addition of an origin of conjugatinal transfer to the plasmids.

Colicins↗
PubMed1977

Analysis of the role of recombination and repair in mutagenesis of Escherichia coli by UV irradiation.

Multiple mutant strains have been tested or their mimicry of the UV-mutagenesis deficiency of a recA single mutant. Revertants to histidine prototrophy and clear plaque mutants of lambda were scored to determine capacity for UV-mutagenesis. Nearly normal capacity was shown by a uvr+ recB- recF- strain, which shows almost no recA-dependent recombination, by uvr- recB+ recF- strains, which show almost no recA-dependent repair and by a uvrA- recB- recF- strain, which shows neither recA-dependent recombination nor repair. Since the uvr mutants can be assumed to show additionally no excision repair, these results may mean that UV-mutagenesis occurs during processes other than recombination and repair. Alternative hypotheses are discussed. The slight difference in mutagenic capacity was traced to the recF single mutation, which blocks the production of unmixed bursts of clear-plaque lambda mutants. Since this accounts for only about 10% of the mutations leading to clear-plaque mutants, it is suggested that there is more than one UV-mutagenic process.

Coliphages↗
PubMed1977

Heteroduplex analysis of tra delta f' plasmids and the mechanism of their formation.

Four tra delta FargG+ plasmids, derived from matings between Hfr AB312 and a recA recipient, have been shown to have deletions of at least 50% of the F genome, including the region in which the tra genes map. The mutant plasmids do contain the F genes required for plasmid maintenance. Correlations can be made between, on the one hand, the F genes present on the tradelta F' plasmids and the F genes transferred early by an Hfr donor, and, on the other hand, the F genes deleted from the tradelta F' plasmids and the F genes transferred late by an Hfr donor. A biased representation of proximally and distally transferred chromosomal markers among the tradelta F' elements was also demonstrated. Taken Taken together, the asymmetrical representation of Hfr genes and the cis dominance of the Tra phenotype of these mutants can best be explained by the hypothesis that the tradelta F' plasmids are formed by repliconation of the transferred exogenote in a recA recipient.

Chromosome Mapping↗
PubMed1977

Genetic mapping of the F plasmid gene that promotes degradation of stable ribonucleic acid in Escherichia coli.

F+ Escherichi coli cells that contain an srnA mutant allele degrade their stable ribonucleic acid (RNA) extensively after RNA synthesis is blocked at 42 degrees C. The relevant gene promoting degradation of stable RNA, srnB+, or its promoter was mapped between 1.7 and 2.8 kilobases on the F plasmid by using deleted F' plasmids and chimeric plasmids composed of pSC101 and fragments of F plasmid.

Chromosomes, Bacterial↗
PubMed1976

Molecular cloning of DNA from F sex factor of Escherichia coli K-12.

We describe the molecular cloning of various DNA segments generated by partial EcoRI endonuclease digestion of the sex factor F. These segments have been analyzed by agarose gel electrophoresis of EcoRI digests and were arranged in a series of overlapping fragments using the EcoRI fragment map of F established by H. Ohtsubo and E. Ohtsubo. The clones isolated demonstrate one or more of the following F-specified functions: inhibition of female-specific phage (T7) multiplication, formation of F pili, surface exclusion, or immunity to lethal zygosis. These properties are discussed in terms of the EcoRI fragments of F that specify them.

Coliphages↗
PubMed1976

cis-Dominant, transfer-deficient mutants of the Escherichia coli K-12 F sex factor.

Rare conjugational progeny formed by crossing each of five Hfr strains with a recA-F- strain have been characterized. Selection was made for a proximal Hfr marker, taking strict precautions to prevent transfer of recA+ to the zygotes. Most of the progeny were found to be F' strains containing deletion mutant plasmids. With two exceptions, these mutant plasmids have lost all of the tra genes, which are required to confer conjugational donor ability upon a host. In addition, all but the exceptional mutant plasmids were found to be very poorly transmissible from transient heterozygotes which also contain a wild-type F' plasmid. The poor transmissibility is a cis-dominant transfer-defective phenotype which may result from deletion of all or part of the origin of transfer replication (ori), or of a gene determining a cis-acting protein. The two exceptional mutant plasmids may carry short deletions of some of the tra genes or polar tra mutations. The remaining progeny were nonmutant F' strains and F- strains. The frequency with which the F- strains were recovered permits us to estimate that the maximum amount of recombination possible in a recA56 zygote is 10(-6) that of a recA+ zygote.

Conjugation, Genetic↗
PubMed1976

Purification and properties of two deoxyribonucleases of Pseudomonas aeruginosa.

A survey of the major deoxyribonucleases in Pseudomonas aeruginosa strain PAO was undertaken. Two activities predominated in Brij-58 lysates of this organism. These have been purified from contaminating nuclease activities, and some of their properties have been elucidated. The first was a nuclease that degraded heat-denatured deoxyribonucleic acid (DNA) to mono- and dinucleotides. The activity of this enzyme was confined to single-stranded DNA, and 100% of the substrate was hydrolyzed to acid-soluble material. The Mg2+ optimum is low (1 to 3mM), and the molecular weight is 6 X 10(4). The second predominant activity was an adenosine 5'-triphosphate (ATP)-dependent deoxyribonuclease. This enzyme had an absolute dependence on the presence of ATP Mg2+ concentrations of approximately 10 mM. Five moles of ATP was consumed for each mole of phosphodiester bonds cleaved. The acid-soluble products of the reaction consisted of short oligonucleotides from one to six bases in length. Only 50% of the double-stranded DNA was rendered acid soluble in a limit digest. The molecular weight of this enzyme is 3 X 10(5). The observation of these enzymes in P. aeruginosa is consistent with the possibility that recombinational pathways similar to those of Escherichia coli are operating in this organism.

Adenosine Triphosphate↗
PubMed1974

Isolation of exonuclease VIII: the enzyme associated with sbcA indirect suppressor.

recB and/or recC deficiency in Escherichia coli K-12 is indirectly suppressed by the presence of sbcA(-) mutations. sbcA(-) strains contain an increased level of an ATP-independent nuclease. Genetic and enzymatic tests indicate that this activity is not exonuclease III, exonuclease V (recB-recC nuclease), DNA polymerase I, or lambda exonuclease. This new enzyme (exonuclease VIII) has been purified 750-fold and shows a striking preference for double-stranded DNA over heat-denatured DNA. It does not act endonucleolytically on closed circular, single-stranded DNA as exonuclease V does. It also lacks a 3'-phosphatase function. Analysis on sodium dodecyl sulfate-polyacrylamide gels indicates that exonuclease VIII is not present in unsuppressed (sbcA(+)) strains. It is thought that sbcA determines some type of control function; the structural gene for exonuclease VIII is denoted by recE.

Chromatography, DEAE-Cellulose↗
PubMed1974

Genetic analysis of a double male strain of Escherichia coli K12.

The behavior of a double male strain of Escherichia coli K12 has been compared to that of its parents and a primary F' strain carrying F14 in order to determine whether the genome of the double male, responsible for the double origin mode of gene transmission, is composed of one or two linkage groups. F-prime plasmids carrying leu and pyrB and argG and metC have been detected following mating an F(-)recA(-) recipient with the double male. Their existence strongly supports the contention that the double male is composed of a single linkage group with two integrated sex factors. Data from acridine orange curing experiments places the frequency of double male cells in the population of growing cells in the two-chromosome configuration as less than one percent. Evidence for a unique origin and terminus of DNA replication deduced by the density labelling and transduction of double male DNA supports the contention that the double male is best considered a cell with a single chromosome carrying two integrated F plasmids.

Acridines↗