Biomedical subjects

J J Pritchard

Publications and source records attributed to J J Pritchard.

13 recordsLinked to original sources

PubMed1980

Host components required for the replication of the resistance plasmid R124 and a copy mutant derivative.

The replication of R124, and a copy mutant derivative of it, was measured with respect to dependence on the host DnaA, DnaB, DnaC, DnaE, DnaG, and PolA gene products. Both plasmids replicated under conditions where the DnaA gene product was inactivated or where the polymerising activity of the PolA gene product was reduced. In contrast, neither plasmid replicated to any appreciable extent, if the DnaB, DnaC, DnaE or DnaG gene products were inactivated. R124 integratively suppressed the lesion of the dnaA mutant but the copy mutant derivative had only a very weak suppressing effect. Neither plasmid suppressed the lesions of any of the other dna mutants.

Bacterial Proteins↗

PubMed1979

Factors influencing the copy number of F-like plasmids in Escherichia coli and Salmonella typhimurium.

The copy numbers of Flac, four F-like plasmids and pLT2 were estimated in two strains of Salmonella typhimurium and (for all except pLT2) one strain of Escherichia coli. For organisms grown in casamino acids minimal medium, the plasmids spanned a 7--8 fold range of copy number with ColB-K98 having the highest copy number in each strain and R124 the lowest. The copy number of ColB-K98 was substantially greater than 1 in each of the strains tested. There was no clear relation between the plasmid size and copy number, although the plasmids studied spanned only a narrow size range. The copy number of individual plasmids was slightly reduced or not affected at all by the presence of a second plasmid in the same strain. Derivatives harbouring each of the plasmids were grown in three different media to ascertain how plasmid copy number responds to changes in growth rate. For each plasmid, the copy number increased with decreasing growth rate. Extracts from each of the three strains harbouring ColB-K98 contained two distinct plasmid species. One appeared to be about twice as large as the other and both were absent from Col- segregants.

Conjugation, Genetic↗

PubMed1977

A mutant of the antibiotic resistance factor R124 with altered copy number.

A mutation conferring increased antibiotic resistance on Salmonella typhimurium strain 11G carrying R124 was plasmid determined; strains harbouring the mutant plasmid contained more DNA as ccc plasmid than those harbouring R124. The increased copy number was manifested at all growth rates tested.

Anti-Bacterial Agents↗

PubMed1977