Effect ofmutY andmutM/fpg-1 mutations on starvation-associated mutation inEscherichia coli: implications for the role of 7,8-dihydro-8-oxoguanine

Abstract

MutY specifies a DNA glycosylase that removes adenines unnaturally paired with various bases including oxidized derivatives of guanine, such as 7,8-dihydro-8-oxoguanine (8-oxoG). The rate of mutation in starved Escherichia coli cells is markedly raised in mutY mutants defective in this glycosylase. As predicted, the mutations produced include G to T transversions. Bacteria carrying mutM or fpg-1 mutations (defective in Fapy glycosylase, which removes oxidized guanine residues such as 8-oxoG) show little or no enhancement of mutation under starvation conditions. When present together with mutY, however, mutM clearly further enhances the rate of mutation in starved cells. Plasmids resulting in overproduction of MutY or Fapy glycosylases reduce the rate of mutation in starved cells. We conclude that, in non-growing bacteria, oxidized guanine residues, including 8-oxoG, constitute an important component of spontaneous mutation. Addition of catalase to the plates did not reduce the mutant yield, indicating that extracellular hydrogen peroxide is not involved in the production of the premutational damage. Singlet oxygen, known to give rise to 8-oxoG, may be the ultimate oxidative species.

Multiprobe RNase Protection Assay Analysis of mRNA Levels for the Escherichia coli Oxidative DNA Glycosylase Genes under Conditions of Oxidative Stress

“…Since cells are experiencing more oxidative stress during exponential growth, it may make sense to have higher levels of enzymes that repair oxidative DNA damage present during this time. In possible disagreement with this, it has been calculated that the rate of production of the common oxidative damage 8-oxoG in the DNA of starved cells is threefold greater than in the DNA of growing cells (7). It has been shown that the mismatch repair protein MutL becomes limiting for mismatch repair during stationary phase, and it has been speculated that this could allow cells to regulate their potential to evolve (22).…”

A DNA Polymerase V Homologue Encoded by TOL Plasmid pWW0 Confers Evolutionary Fitness on Pseudomonas putida under Conditions of Environmental Stress

“…Some data published already more than 20 years ago indicate that freeze-thaw stress and drying cycles can also cause DNA damage which is mutagenic to a bacterium (3,10,65,73). It has also been shown that oxidative DNA damage generated from endogenous metabolism in growth-arrested cells accumulates during stasis (7,8).In Escherichia coli, DNA polymerases Pol II, Pol IV, and Pol V are induced as part of the SOS regulon in response to DNA damage (23). The LexA repressor binds to a 20-bp consensus sequence in the operator region of the SOS regulon genes, suppressing their expression.…”

Regulation of mutY and Nature of Mutator Mutations in Escherichia coli Populations under Nutrient Limitation

“…The genes mutM and mutY are involved in this process, but mutM changes are only weakly mutagenic (2). Hence the mutational spectrum under glucose limitation was most likely a function of mutY regulation or mutation.…”

“…mutY was shown to be the first gene in an operon and to be regulated by aerobiosis, but not by oxygen stress regulators (10,11). Also, the effect of mutM and mutY on stationaryphase, starvation-associated mutation indicated that mutY, but not mutM, mutants increase mutation rates under these conditions (2). The regulation of these genes by steady-state nutrient limitation was not previously studied, and to observe whether control of mutY was responsible for the spectrum of mutations in chemostat cultures, the expression of mutY needed to be studied under steady-state nutrient limitation.…”