Mutational specificity of glyoxal, a product of DNA oxidation, in the lacI gene of wild-type Escherichia coli W3110

Abstract

To determine the mutation spectrum of glyoxal, which is produced from DNA by oxygen free-radicals, we analyzed the chromosomal lacI gene of mutants induced by treatment of a wild-type Escherichia coli strain with glyoxal. The cell death and the mutation frequency increased according to the concentration of glyoxal added to the culture medium. The majority of the spontaneous mutations (82%) and that of the glyoxal-induced mutations (50%) were the addition or deletion of a 5′-TGGC-3′ sequence at positions 623–634, which was reported to be a mutational hot spot in the lacI gene. In the glyoxal-induced mutants, however, the ratio of base-pair substitutions was increased (35%). Although all types of base-pair substitutions were detected, 78% of the base-pair substitutions occurred at G:C sites. Among them, G:C→A:T transitions were predominant, followed by G:C→T:A transversions. These mutations appeared to be distributed randomly within the lacI gene. These results suggest that glyoxal-induced mutations may correlate to mutations induced by oxygen free-radicals.