Ultraviolet mutagenesis and inducible DNA repair in Caulobacter crescentus

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Abstract
The ability to reactivate ultraviolet (UV) damaged phage ΦCbK (W-reactivation) is induced by UV irradiation of Caulobacter crescentus cells. Induction of W-reactivation potential is specific for phage ΦCbK, requires protein synthesis, and is greatly reduced in the presence of the rec-526 mutation. The induction signal generated by UV irradiation is transient, lasting about 1 1/2–2 h at 30°C; if chloramphenicol is present during early times after UV irradiation, induction of W-reactivation does not occur. Induction is maximal when cells are exposed to 5–10 J/m2 of UV, a dose that also results in considerable mutagenesis of the cells. Taken together, these observations demonstrate the existence of a UV inducible, protein synthesis requiring, transiently signalled, rec-requiring DNA repair system analogous to W-reactivation in Escherichia coli. In addition, C. crescentus also has an efficient photoreactivation system that reverses UV damage in the presence of strong visible light.