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  • Title: Weigle reactivation of phage lambda in a recA mutant of Escherichia coli: dependence on the excess amounts of photoreactivating enzyme in the dark.
    Author: Yamamoto K, Shinagawa H.
    Journal: Mutat Res; 1985 May; 145(3):137-44. PubMed ID: 3157057.
    Abstract:
    The plating efficiency of ultraviolet-light-irradiated phage lambda in the dark is increased when an Escherichia coli recA host, which is transformed with a multicopy plasmid, pKY1, carrying the phr gene of E. coli, is irradiated with 254 nm UV prior to infection (Weigle (W) reactivation). Such W reactivation in lexA3 and umuC strains, with or without pKY1, is almost undetectable. Addition of umu mutations to recA56/pKY1 cells blocks this process, but addition of the lexA3 mutation instead gives high levels of W reactivation. Fusion of the lacZ gene with recA or umuC promoters permitted measurement of the effects of UV radiation on transcription of these SOS operons for various mutated cells, with and without the phr+ plasmid. The presence of the recA56 allele totally abolishes UV induction of both recA and umuC gene expression in the cells, both with and without the plasmid. Thus, the observed W reactivation in the recA strain carrying the phr+ plasmid requires only the constitutive amount of the Umu proteins, and does not require the lexA+ recA+-dependent inducible process. While we observed an increase in the W reactivation of UV-irradiated lambda phage in a recA56/pKY1 cell, there is no corresponding mutagenesis of the UV-irradiated phage in UV-irradiated cells. We propose that the E. coli phr gene product facilitates error-free pathways of DNA repair in the absence of photoreactivation. The fact that a recA/pKY1 strain permits almost normal levels of W reactivation, but completely blocks W mutagenesis, leads us further to suggest that the recA gene product, in general, functions in a regulatory manner in W reactivation and in both regulatory and mechanistic ways in W mutagenesis.
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