Translesion synthesis is the main component of SOS repair in bacteriophage lambda DNA

Abstract

Agents that interfere with DNA replication in Escherichia coli induce physiological adaptations that increase the probability of survival after DNA damage and the frequency of mutants among the survivors (the SOS response). Such agents also increase the survival rate and mutation frequency of irradiated bacteriophage after infection of treated bacteria, a phenomenon known as Weigle reactivation. In UV-irradiated single-stranded DNA phage, Weigle reactivation is thought to occur via induced, error-prone replication through template lesions (translesion synthesis [P. Caillet-Fauquet, M. Defais, and M. Radman, J. Mol. Biol. 117:95-112, 1977]). Weigle reactivation occurs with higher efficiency in double-stranded DNA phages such as X, and we therefore asked if another process, recombination between partially replicated daughter molecules, plays a major role in this case. To distinguish between translesion synthesis and recombinational repair, we studied the early replication of UV-irradiated bacteriophage X in SOS-induced and uninduced bacteria. To avoid complications arising from excision of UV lesions, we used bacterial uvrA mutants, in which such excision does not occur. Our evidence suggests that translesion synthesis is the primary component of Weigle reactivation of X phage in the absence of excision repair. The greater efficiency in Weigle reactivation of double-stranded DNA phage could thus be attributed to some inducible excision repair unable to occur on single-stranded DNA. In addition, after irradiation, X phage replication seems to switch prematurely from the theta mode to the rolling circle mode.Exposure of Escherichia coli to agents that interfere with DNA replication leads to RecA-mediated cleavage of the LexA repressor, which induces a number of diverse physiological functions called the SOS response (32,45). Among the multiple functions expressed during this response is a transient error-prone DNA processing event that seems to be responsible for most of the radiation-or chemical-induced mutagenesis (42). This phenomenon requires RecA-mediated cleavage of the UmuD protein and formation of a complex between the COOH fragment and the UmuC protein (3, 31, 37). The UmuDC complex may act by facilitating replication with a high level of misincorporation past noninstructive lesions in the DNA (2). Mutagenesis is observed not only on the bacterial chromosome but also on extrachromosomal DNA, and it can easily be studied using viruses as probes (14). Induction of the host SOS response results in an increased survival of UV-irradiated bacteriophage (Weigle reactivation), which is accompanied by an increased mutation frequency in the progeny (13, 43). Genetic and biochemical evidence indicates that in singlestranded DNA phage, Weigle reactivation occurs via induced replication through the UV lesions (translesion synthesis) (6). Moreover in vitro studies of the extent of DNA synthesis on UV-irradiated XX174 DNA have shown a large increase in the turnover of nucleoside triphosphates to free monophosphates throu...

UvsX Recombinase and Dda Helicase Rescue Stalled Bacteriophage T4 DNA Replication Forks in Vitro

“…Despite several decades of vigorous exploration of T4 repair mechanisms, there is a striking absence of any report of the kind of break-reunion recombination repair so well characterized in E. coli. In phage , which relies upon E. coli repair systems, as many as 20 dimers/genome were insufficient to block viral DNA replication in an unirradiated, excision-deficient E. coli cell in which the recA-dependent recombination functions were not induced and in which few recombinational exchanges occurred (41). This high survival seems unlikely to have been simple translesion synthesis because there is little mutagenesis in UV light-irradiated phage in the absence of UV irradiation of the host (42); absent the induced level of classical recombination repair, the mechanism may have been replication repair.…”

SOS repair can be about as effective for single-stranded DNA as for double-stranded DNA and even more so

“…That is particularly significant for it shows that while nearly all the lethal lesions in dsDNA are repair- Ironically, the incorrect idea that dsDNA is more efficiently repaired by Weigle reactivation than ssDNA had the beneficial effect of stimulating an important study showing that recombinational repair contributes an insignificant amount to the SOS repair of UV-irradiated lambda relative to the contribution of translesion synthesis (5). Although an additional conclusion, namely, that inducible excision repair makes Weigle reactivation more efficient for dsDNA than for ssDNA, now appears to be unfounded, it should nevertheless prompt us to wonder why it is that Weigle reactivation is not more efficient for dsDNA.…”

“…It has also been suggested that Weigle mutagenesis occurs in dsDNA with a higher efficiency than in ssDNA (4,5).…”

Mutation and Dna Repair: From the Green Pamphlet to 2005

“…Because the former mechanism could not be detected in yeast (Resnick, Boyce & Cox, 1981), and because proteins involved in T4 DNA transactions are more closely related to those in archaea and eukaryotes, it is possible that the eubacteria perform most of their recombination repair differently from organisms in the other two domains. It is also possible that E. coli does indeed carry out some replication repair, because inactivating the E. coli recA system still allows numerous lesions to be survived in phage (Defais et al, 1989), and because of ingenious genetic evidence that supports the operation of replication repair (Ozgenc, Szekeres & Lawrence, 2005).…”