A number of metal compounds have been shown to be human carcinogens. Others, while not proven human carcinogens, are able to cause tumors in laboratory animals. Short-term bacterial assays for genotoxic effects have not been successful in predicting the carcinogenicity of metal compounds. We report
Induction of prophage λ during the division cycle ofEscherichia coli
✍ Scribed by Michael J. Worsey; Brian M. Wilkins
- Publisher
- Springer
- Year
- 1975
- Tongue
- English
- Weight
- 650 KB
- Volume
- 139
- Category
- Article
- ISSN
- 1617-4615
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✦ Synopsis
When synchronous populations of Escherichia coli B/r (lambda) were exposed to low doses of ultraviolet light, the yield of infective centres varied with cell age. The yield was highest if the lysogenic bacteria were irradiated at a time which coincides approximately with the termination of rounds of DNA replication and it was lowest when dividing cells were irradiated. No such variation was detected following either irradiation of excision-defective lysogenic cells or thermal induction of lambdacI857 prophage in irradiated bacteria. It is suggested that the variation reflects a relationship between prophage induction and inhibition of cell division. This hypothesis is supported by data showing that irradiation promoted induction and curtailed division in E. coli K12 dnaA mutants which were dividing in the absence of DNA replication.
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Escherichia coli strains B5 and B/r/l were grown under conditions of periodic glucose starvation in a minimal medium. Such conditions of growth give rise to two synchronous populations that are out of phase regarding their time of division, one dividing shortly after a new supply of fresh medium and
We have followed, by DNA-DNA hybridization, the variation in the number of copies of prophage P1 relative to two chromosomal markers when the doubling time of the host cells is modified by a change in carbon source. The ratio of P1/chromosome terminus undergoes a twofold decrease when the cell doubl