Biomedical subjects
Publications and source records attributed to P Caillet-Fauquet.
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Preincubation at 42 degrees, before infection at permissive temperature by phage lambda, of an Escherichia coli dnaB mutant, provokes a significant increase in survival and mutagenesis of ultraviolet irradiated phage as well as mutagenesis of untreated phage. Similarly to UV irradiation and many chemical mutagens, the inhibition of DNA synthesis by temperature shift of this dnaB mutant induces SOS repair. This work shows that replication blockage in bacterial DNA is not only mutagenic for bacterial DNA itself (Witkin, 1975) but also for normally replicating lambda DNA, probably due to induction of diffusible products.
Phage production in liquid medium during W-reactivation parallels the extent of W-reactivation of infective centres on plates. The mean burst size is independent of W-reactivation; thus the reactivated phage yields a normal burst. As 8 plates, the lex- mutant shows no W-reactivation in liquid medium. It is concluded that W-reactivation is a consequence of an induced DNA repair which reactivates the damaged parental phage DNA to its full biological activity.
Ultraviolet mutagenesis of phage gamma is produced by host functions which are inducible by ultraviolet irradiation of the host cell. Induction kinetics and the half life of the inducible mutagenic DNA repair (SOS-repair) in E.coli have been determined using phage gamma assays. At 37 degrees C, both mutagenic and repair activities are maximal approximately 30 min following irradiation and decay with a half life of approximately 30 min. The presence of 100 mug/ml chloramphenicol during the first 40 min after irradiation completely abolishes induction of repair and mutagenesis. The ultraviolet induction pattern of SOS repair very much resembles that of gamma prophage in lysogenic induction (Monk and Kinross, 1975).
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Regulation of genetic stability is discussed in terms of interactions between constitutive and inducible DNA repair processes with specific emphasis on the results of our experimental studies of mismatch correction and SOS induction in Escherichia coli.
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