Multiple pathways for SOS-induced mutagenesis in Escherichia coli : An overexpression of dinB / dinP results in strongly enhancing mutagenesis in the absence of any exogenous treatment to damage DNA

Abstract

ABSTRACTdinP is an Escherichia coli gene recently identified at 5.5 min of the genetic map, whose product shows a similarity in amino acid sequence to the E. coli UmuC protein involved in DNA damage-induced mutagenesis. In this paper we show that the gene is identical to dinB, an SOS gene previously localized near the lac locus at 8 min, the function of which was shown to be required for mutagenesis of nonirradiated phage infecting UV-preirradiated bacterial cells (termed UTM for untargeted mutagenesis). A newly constructed dinP null mutant exhibited the same defect for UTM as observed previously with a dinB::Mu mutant, and the defect was complemented by plasmids carrying dinP as the only intact bacterial gene. Furthermore, merely increasing the dinP gene expression, without UV irradiation or any other DNAdamaging treatment, resulted in a strong enhancement of mutagenesis in Flac plasmids; at most, 800-fold increase in the G6-to-G5 change. The enhanced mutagenesis did not depend on recA, uvrA, or umuDC. Thus, our results establish that E. coli has at least two distinct pathways for SOS-induced mutagenesis: one dependent on umuDC and the other on dinB͞P.

Escherichia coli DNA polymerase IV contributes to spontaneous mutagenesis at coding sequences but not microsatellite alleles

“…Further analyses showed no strain difference in the types of mutational events at the repeat allele. This result was surprising to us, as Pol IV was shown to create -1 frameshifts in homopolymeric G 6 runs [22]. The difference between our study and the previous study [22] could be due to sequence context effects (lac gene vs. HSV-tk gene) or the length of the repetitive target (6 vs. 10 nucleotides).…”

“…coli polymerase IV is a distributive polymerase that lacks a 3'to 5' exonuclease (proofreading) activity and is prone to elongation of misaligned primer/template structures [20]. The overespression of the polymerase causes -1 frameshifts in polypurine runs of G in undamaged DNA [22]. When looking at spontaneous mutagenesis, previous studies have shown a statistically significant decrease in the number of frameshift and base substitution events in the absence of dinB [23,24,32] while overexpression of the dinB gene results in a significant increase in the mutation frequency [21,22].…”

“…The overespression of the polymerase causes -1 frameshifts in polypurine runs of G in undamaged DNA [22]. When looking at spontaneous mutagenesis, previous studies have shown a statistically significant decrease in the number of frameshift and base substitution events in the absence of dinB [23,24,32] while overexpression of the dinB gene results in a significant increase in the mutation frequency [21,22]. Pol IV was chosen as a candidate to analyze for strand slippage within microsatellite alleles because a role for the polymerase in spontaneous mutagenesis was acknowledged, as was its role in mutagenesis at homoploymeric G sequences.…”

“…Pol IV does not require recA, umuDC, uvrA, polA or polB for activity [21,22] and errors made by Pol IV are correctable by MMR, suggesting Pol IV contributes to replication errors on undamaged templates [21]. Expression of the dinB gene has been shown to cause an increase in -1 frameshifts [21,23] as well as single nucleotide base substitutions with a preference toward G:C bases.…”

Proficient and Accurate Bypass of Persistent DNA Lesions by DinB DNA Polymerases

“…Spontaneous mutagenesis induced by overexpression of DinB exhibits a strong preference for -1 frameshift mutations, but also a substantial increase in certain base substitution mutations at purines. 16 Moreover, treatment with 4-NQO dramatically increases the frequency of -1 frameshift mutations observed. Despite the relative ambiguity of these phenomena, they laid the foundation, particularly in concert with the known mutagenic phenotypes of the dinB homolog umuC, for a view of dinB as an agent of mutation.…”