EFFECT OF MUTY AND MUTM FPG-1 MUTATIONS ON STARVATION-ASSOCIATED MUTATION IN ESCHERICHIA-COLI - IMPLICATIONS FOR THE ROLE OF 7,8-DIHYDRO-8-OXOGUANINE/

MutY specifies a DNA glycosylase that removes adenines unnaturally pai red 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 i n 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 cond itions. 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 mutati on in starved cells. We conclude that, in non-growing bacteria, oxidiz ed guanine residues, including 8-oxoG, constitute an important compone nt of spontaneous mutation. Addition of catalase to the plates did not reduce the mutant yield, indicating that extracellular hydrogen perox ide is not involved in the production of the premutational damage. Sin glet oxygen, known to give rise to 8-oxoG, may be the ultimate oxidati ve species.