engleski

RecBC(D) enzyme in UV-irradiated E. coli interferes with lambda prophage recombinogenicity

RecBCD enzyme is involved in the radiation-induced process known as prophage inactivation (1). The process leads to the inability of lambda prophage to excise itself from the E. coli chromosome via site-specific recombination (2). In this work we wanted to further characterize the role of RecBCD enzyme in this process. In addition, we examined the ability of irradiated prophage to recombine with the infecting homologous phage. We used several E. coli mutants differentially altered in the RecBCD's activities. The results showed that in the mutants carrying either recB2109 or recD1903, which do not exhibit considerable nuclease activities, the prophage progressively loses its capacity for both site-specific and general recombination. In the recB268 null mutant, however, prophage recombinogenicity remained preserved. We also showed that the prophage unable to recombine remained transcribable and that the recombination frequencies in phage x phage crosses were not affected by postirradiation incubation. Our results suggest that the helicase activity of RecBCD is responsible for the loss of prophage recombinogenicity. This loss is most probably a consequence of the unsuccessful RecBC(D)-dependent recombinational repair of damaged cell chromosome, which may produce intermediates unsuitable for further recombination reactions. Such intermediates, when having reached the prophage, may affect its recombinogenicity. (1) Petranović et al., Mol. Gen. Genet. 196, (1984) 167. (2) Medić-Petranović et al., Int. J. Radiat. Biol. 32, (1977) 103.

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