Role of DnaB helicase in UV-induced illegitimate recombination in Escherichia coli.
To study the involvement of DNA replication in UV-induced illegitimate recombination, we examined the effect of temperature-sensitive dnaB mutations on illegitimate recombination and found that the frequency of illegitimate recombination was reduced by an elongation-deficient mutation, dnaB14, but not by an initiation-deficient mutation, dnaB252. This result indicates that DNA replication is required for UV-induced illegitimate recombination. In addition, the dnaB14 mutation also affected spontaneous or UV-induced illegitimate recombination enhanced by the recQ mutation. Nucleotide sequence analyses of the recombination junctions showed that DnaB-mediated illegitimate recombination is short homology dependent. Previously, Michel et al. (B. Michel, S. Ehrlich, and M. Uzest, EMBO J. 16:430--438, 1997) showed that thermal treatment of the temperature-sensitive dnaB8 mutant induces double-stranded breaks, implying that induction of illegitimate recombination occurs. To explain the discrepancy between the observations, we propose a model for DnaB function, in which the dnaB mutations may exhibit two types of responses, early and late responses, for double-stranded break formation. In the early response, replication forks stall at damaged DNA, resulting in the formation of double-stranded breaks, and the dnaB14 mutation reduces the double-stranded breaks shortly after temperature shift-up. On the other hand, in the late response, the arrested replication forks mediated by the dnaB8 mutation may induce double-stranded breaks after prolonged incubation.
Hanada
K
K
The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan.
Yamashita
T
T
Shobuike
Y
Y
Ikeda
H
H
D001426:Bacterial Proteins; D004249:DNA Damage; D004265:DNA Helicases / Q000235:genetics / Q000502:physiology*; D004269:DNA, Bacterial / Q000737:chemistry; D053488:DnaB Helicases; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000528:radiation effects; D009154:Mutation; D011995:Recombination, Genetic / Q000528:radiation effects*; D017422:Sequence Analysis, DNA; D014466:Ultraviolet Rays
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004265:DNA Helicases; D053488:DnaB Helicases