Phage-lambda-mediated transduction of non-conjugative plasmids is promoted by transposons.
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Bacteriophage lambda↗
Biomedical subjects
O Fayet
Publications and source records attributed to O Fayet.
Map position of the replication origin on the E. coli chromosome.
Strains carrying a dnaA temperature sensitive (t.s.) mutation and a Mu-1 prophage inserted within different genes near the origin of replication have been constructed. For each strain, integratively suppressed Hfrs, named G and D in which the ori region was replicated clockwise and counterclockwise respectively, were isolated. The strand preferences of Mu-1 specific Okazaki fragments were subsequently determined for each t.s. strain and its Hfr derivatives. Their comparison led us to establish the direction of replication of the Mu-1 marker from ori. The site ori was confined to the bglB-C--rbsK-P interval.
Chromosome Mapping↗
Complex phenotypes of null mutations in the htr genes, whose products are essential for Escherichia coli growth at elevated temperatures.
Transposon insertion, followed by screening, has allowed the identification of a set of genes, called htr, whose products are required for Escherichia coli growth at elevated temperatures. The htrB gene has been shown to map at 23.5 min on the E. coli genetic map. It codes for a very basic, hydrophobic, 35,000-Mr polypeptide, possessing a putative membrane-spanning domain. At the non-permissive temperature, htrB mutant bacteria stop dividing, followed by the formation of bulges and eventual lysis. The htrC gene maps at 90 min, is under sigma 32 regulation and codes for a 21, 130-Mr polypeptide. At 43 degrees C, htrC mutant bacteria gradually lyse, whereas at intermediate temperatures they filament extensively. Finally, the htrM gene maps at 81 min, is under sigma 32 regulation and codes for a 35,000-Mr polypeptide. The HtrM null phenotype included inability to grow above 42 degrees C, extreme mucoidness and sensitivity to bile salts, even at the permissive temperatures. The htrM gene is identical to the rfaD gene, whose product is required for the biosynthesis of the lipopolysaccharide precursor ADP-L-glycero-D-mannoheptose (Pegues et al., J. Bact., 1990, 172, 4652-4660).
Bacterial Proteins↗
[Enzymatic profile and plasmid content of Neisseria polysacchareae].
The enzymatic profile of "Neisseria polysacchareae" was determined by using chromogenic substrate (API System), and was compared to that of N. meningitidis, N. gonorrhoeae and N. lactamica. The tested classes of enzymes were aminopeptidase, proteases, esterases, lipases, glycosidases, phosphatase and phosphoamidase. "N. polysacchareae" exhibited various aminopeptidase and protease activities and a strong esterase activity. No lipase and glycosidase activities were detected by the tested substrates. The strains of "N. polysacchareae" differed from that of N. meningitidis in the presence of hydroxyproline aminopeptidase and the lack of gamma-glutamyl-transferase activity. Five strains harboured extrachromosomal elements. The plasmids were of 4.2 Kb in size in four cases and of more than 40 Kb in four cases. Three strains simultaneously harboured these two plasmids. This plasmid content is another characteristic of strains of this new taxon. No phenotypic modification was observed in plasmid-containing strains.
DNA↗
[Presence of plasmids in Neisseria meningitidis].
The plasmid content of twenty-nine Neisseria meningitidis strains, isolated from CSF and blood cultures, was investigated by agarose gel electrophoresis. The strains (twenty-seven from serogroup B and two from serogroup C) were sensitive to antibiotics, but 50% were resistant to sulphonamide (MIC greater than or equal to 16 mg/l). Two serogroup-B strains from CSF harboured an extrachromosomal element. These two cryptic plasmids differed in size: 8.4 Kb for pNMT1 and 82 Kb for pNMT2.
DNA Restriction Enzymes↗
DNA modification in Neisseria gonorrhoeae: resistance of DNA of 19 strains to cleavage by restriction enzymes.
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DNA (Cytosine-5-)-Methyltransferases↗
Susceptibility of Neisseria gonorrhoeae DNA to cleavage by restriction endonuclease KpnI.
We compared the susceptibility of Escherichia coli and Neisseria gonorrhoeae DNA to cleavage by KpnI and found that KpnI has a lower affinity for gonococcal DNA. Site-specific methylation is suggested as the cause of this altered affinity.
DNA (Cytosine-5-)-Methyltransferases↗
Upstream stimulators for recoding.
Recent progress in elucidation of 5' stimulatory elements for translational recoding is reviewed. A 5' Shine-Dalgarno sequence increases both +1 and -1 frameshift efficiency in several genes; examples cited include the E. coli prfB gene encoding release factor 2 and the dnaX gene encoding the gamma and tau subunits of DNA polymerase III holoenzyme. The spacing between the Shine-Dalgarno sequence and the shift site is critical in both the +1 and -1 frameshift cassettes; however, the optimal spacing is quite different in the two cases. A frameshift in a mammalian chromosomal gene, ornithine decarboxylase antizyme, has recently been reported; 5' sequences have been shown to be vital for this frameshift event. Escherichia coli bacteriophage T4 gene 60 encodes a subunit of its type II DNA topoisomerase. The mature gene 60 mRNA contains an internal 50 nucleotide region that appears to be bypassed during translation. A 16 amino acid domain of the nascent peptide is necessary for this bypass to occur.
Animals↗