The nature of the transfer inhibitor of several F-like plasmids.
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Ampicillin↗
Biomedical subjects
N Willetts
Publications and source records attributed to N Willetts.
The relationship between the transfer systems of some bacterial plasmids.
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Coliphages↗
Genetic and physicochemical characterization of Escherichia coli strains carrying fused F' elements derived from KLF1 and F57.
Although the two F' elements, F57 (carrying his(+)) and KLF1 (carrying leu(+)), cannot normally coexist in the same cell, crosses between RecA(-) strains of Escherichia coli carrying these two elements gave rise, at a low frequency, to progeny carrying both the his(+) and leu(+) markers in an extrachromosomal state. Genetic studies showed that the his(+) and leu(+) markers were now linked, and centrifugation studies of F' DNA isolated from these strains confirmed the presence of a new species of DNA molecule of altered size. It is proposed that the his(+) and leu(+) genes in these strains are covalently linked on a single "fused" F' element.
Acridines↗
Conjugational complementation analysis of transfer-deficient mutants of Flac in Escherichia coli.
A series of 102 transfer-deficient (tra(-)) mutants of Flac (84 of which have been previously described) were classified as carrying frameshift, amber, ochre, UGA, and nonsuppressible mutations. Techniques were evolved for using cultures of F prime strains as efficient recipients in matings, for measuring the number of (F'/F') heterozygote cells in transient populations, and for measuring complementation between different Flac tra(-) mutants. These techniques were used to define nine tra cistrons and to assign most of the tra(-) mutations to one or other of these.
Bacteriological Techniques↗
Genetic analysis of transfer by the Escherichia coli sex factor F, using P1 transductional complementation.
P1 transduction has been used to perform a complementation analysis of a series of transfer-deficient mutants of Flac. The results define ten cistrons and are consistent with the results of a conjugational analysis presented in an accompanying report. Both sets of results are summarized here. Between them, they define eleven cistrons, traA through traK, necessary for conjugational deoxyribonucleic acid (DNA) transfer. Mutants in traI and traD and some in traG still make F-pili, although traD mutants are resistant to f2 phage; their products may be involved in conjugational DNA metabolism. Other mutants in traG and all mutants in the remaining eight cistrons do not make F-pili. One of these, traJ, may be a control cistron, and the others may specify a biosynthetic pathway responsible for synthesis and modification of the F-pilin subunit protein and its assembly into the F-pilus.
Coliphages↗
Deletion map of the Escherichia coli K-12 sex factor F: the order of eleven transfer cistrons.
A series of Hfr deletion mutants was isolated. These mutants contain deletions which extend from a lambda prophage into an Flac which is integrated into the gal operon. Transfer-deficient deletion mutants were found to fall into four different phenotypic groups when tested for male- and female-specific phage resistance. Conjugational and transductional complementation tests with Flac point mutants deficient in transfer (tra(-)) were performed, and the order of 11 tra cistrons was determined. The tra genes are all located between an F gene for the inhibition of female-specific phages and the transposed lac operon originally carried by the Flac. The order of genes in the Hfr studied was established to be: proC... phi(II) (R)... traJ traA traE traK traB traC traF traH traG traD traI...lac...attlambda...bio.
Chromosome Mapping↗
The genetics of transmissible plasmids.
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Bacteriophages↗
Beginning a genetic analysis of conjugational transfer determined by the F factor in Escherichia coli by isolation and characterization of transfer-deficient mutants.
Eighty-four transfer-deficient mutants of Flac have been isolated; 27 of these bear amber mutations and 1 mutant is temperature-sensitive. All the mutants transfer between 10(-2) and <10(-5)% as well as wild-type Flac, all are curable by acridine orange treatment, and all are resistant to the female-specific phage phi(II). Some of the mutants are partially sensitive to female-specific phage tau. Sixty-three of the mutants are resistant to the male-specific phages f1, f2, and Qbeta; 15 are resistant only to f2; and 6 are sensitive to all three male-specific phages. Most of the mutants are still poor recipients in conjugation, but four of the mutants resistant to f1, f2, and Qbeta have become good recipients. Those mutants resistant to all three male-specific phages do not seem to make F-pili.
Acridines↗