Roles of DNA polymerases V and II in SOS-induced error-prone and error-free repair in Escherichia coli

Abstract

DNA polymerase V, composed of a heterotrimer of the DNA damage-inducible UmuC and UmuD 2 proteins, working in conjunction with RecA, single-stranded DNA (ssDNA)-binding protein (SSB), ␤ sliding clamp, and ␥ clamp loading complex, are responsible for most SOS lesion-targeted mutations in Escherichia coli, by catalyzing translesion synthesis (TLS). DNA polymerase II, the product of the damage-inducible polB (dinA ) gene plays a pivotal role in replication-restart, a process that bypasses DNA damage in an error-free manner. Replication-restart takes place almost immediately after the DNA is damaged (Ϸ2 min post-UV irradiation), whereas TLS occurs after pol V is induced Ϸ50 min later. We discuss recent data for pol V-catalyzed TLS and pol II-catalyzed replicationrestart. Specific roles during TLS for pol V and each of its accessory factors have been recently determined. Although the precise molecular mechanism of pol II-dependent replication-restart remains to be elucidated, it has recently been shown to operate in conjunction with RecFOR and PriA proteins.T wo seemingly unconnected questions arising during the early and mid 1970s were to decipher the biochemical basis of SOS mutagenesis in Escherichia coli, often referred to as SOS errorprone repair (1), and to determine a cellular role for E. coli DNA polymerase II. A tentative link between the two was established when it was determined that pol II was induced as part of the LexA-regulon (2). pol II was subsequently shown to be encoded by the DNA damage-inducible polB (dinA) gene (3-5). A ⌬polB strain shows no measurable UV sensitivity, and SOS-induced mutagenesis occurs at normal levels (6, 7). However, a ⌬polB ⌬umuDC double mutant strain is more sensitive to killing by UV light than either of the single mutant strains, implying that the two SOS-induced polymerases might play compensatory roles in vivo (8).The ability of pols II and V to complement each other does not mean that these activities are functionally redundant, and indeed they are not. pol V is able to copy UV-damaged DNA in a process referred to as error-prone translesion synthesis (TLS). TLS generates mutations targeted specifically to DNA template damage sites (9-12). In contrast, pol II copies chromosomal DNA during error-free replication-restart (8). Although both polymerases are induced by DNA damage, they appear to function on widely disparate time frames-pol II-catalyzed replication-restart occurs 2 min post-UV irradiation whereas pol V-catalyzed TLS begins roughly 50 min later (8). In this paper, we discuss current models for the roles of pol V in TLS and pol II in replication-restart.Coping with DNA Damage in E. coli There are over 40 genes induced on DNA damage in E. coli that have been identified recently by using microarray chip technology (13), of which at least 31 are known to be negatively regulated at the transcriptional level by the LexA protein (14). Many of these genes encode proteins required to repair DNA damage (15). The overriding importance of DNA repair is apparent from the ob...

The Essential C Family DnaE Polymerase Is Error-prone and Efficient at Lesion Bypass

“…These misincorporation rates are 100 -1000-fold higher than those reported for replicative polymerases, such as ␣ subunit from E. coli (10 Ϫ4 to 10 Ϫ5 ) (21). These rates are also higher than those reported for errorfree repair polymerases, such as Pol II (misincorporation efficiency ϳ10 Ϫ4 ) (22)(23)(24). Fig.…”

Niche adaptation and genome expansion in the chlorophyll d -producing cyanobacterium Acaryochloris marina

“…Four of the recA genes are located on four separate plasmids (pREB1, -2, -4, and -5), and the other three are on the main chromosome. Multiple copies of umuD (4x) and umuC (3x), two sets of which are plasmid-encoded, and two putative proteins with a lambda-phage cI motif are also likely correlated with the extra recA (22,24). The presence of multiples copies of recA and related enzymes could account for gene duplication and/or integration of foreign genes that would lead to genome expansion.…”

BapE DNA endonuclease induces an apoptotic-like response to DNA damage in Caulobacter

“…By contrast, cell lysis could be counterproductive in multispecies environments as it would provide the other species with a selective advantage and supply them with additional resources. Such ecological differences may explain why Caulobacter cells undergo apoptotic-like death whereas other species have evolved the lesion bypass pathway in which they excise and replace irreparably damaged DNA with an errorprone polymerase (6,24), trading off cell survival for the cost of passing on dramatically altered genomes. Further support for the analogy between the damage responses of Caulobacter and multicellular eukaryotes comes from the fact that both systems promote cell death by inducing chromosome fragmentation.…”

“…Here we focus on the DNA damage response of Caulobacter crescentus because it lacks known lesion bypass pathways for copying extremely damaged DNA (6) and it has a eukaryotic-like cell cycle in which it replicates its DNA once and only once per cell division (7). Although the DNA damage response is less well characterized in Caulobacter than in other bacteria such as E. coli (8), a recent study identified SidA as an early SOS-induced division inhibitor in C. crescentus (9).…”