W-reactivation (Inducible "SOS" DNA Repair) of double stranded DNA bacteriophage ? and single stranded DNA bacteriophage fd on isogenic rec and uvrB mutants of Escherichia coli K-12
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AuthorNdive, Sammy F.W.
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AbstractThe recA mutant has been shown to be completely recombination deficient and highly UV-sensitive. Also, this mutant is remarkably deficient in inducible "SOS" DNA repair and, consequently it is not UV-mutable and it cannot perform W-reactivation, an inducible non-excision repair dependent enhancement of phage recovery. The recB-recF- double mutant like the recA mutant, is recombination deficient and UV-sensitive. As observed, each of these mutations appear to block an independent pathway of genetic recombination. We are interested in determining how closely the recB-recF- double mutant resembles the recA mutant. In this perspective we looked at the W-reactivation of double stranded bacteriophage ? and single stranded bacteriophage fd. On examining the W-reactivation for phage ?, it is seen that the recB- and recF- mutants separately lead to a reduction of UV-reactivation efficiency but when spliced, the recB-recF- double mutant further leads to a reduction of W-reactivation even though this is still significant in magnitude when compared to the results obtained for the recA mutant. In the recA mutant W-reactivation capability is totally absent. Contrary to our results with bacteriophage ? , the recB- and recF mutants individually show enhanced W-reactivation of fd phage. The double mutant recB-recF- however, shows virtually no UV-reactivation potential. This is the same case for recA- mutant. Host-cell reactivation - an excision repair dependent potential was examined in the fd phage, ? vir and Pl vira. Our results demonstrate that host-cell recovery is non-existent in fd phage. On the other hand, we noticed high levels of phage recovery in ? vir and Pl vira. We have demonstrated that although recB-recF- double mutant closely resembles the recA single mutant in their UV-sensitivity and recombination profile, this resemblance is seen to be parallel when their UV-inducible capability is examined in double stranded bacteriophages. We therefore conclude that there are significant levels of inducible "SOS" DNA repair occurring in the recB- and recF- mutants and not in the double mutant, recB-recF-. This is due to the fact that there are genetic differences in the inducible DNA repair capability of single stranded and double stranded bacteriophages.