MUTATIONAL SPECIFICITY OF GLYOXAL, A PRODUCT OF DNA OXIDATION, IN THELACI GENE OF WILD-TYPE ESCHERICHIA-COLI W3110

To determine the mutation spectrum of glyoxal, which is produced from DNA by oxygen free-radicals, we analyzed the chromosomal lad gene of m utants induced by treatment of a wild-type Escherichia coli strain wit h glyoxal. The cell death and the mutation frequency increased accordi ng to the concentration of glyoxal added to the culture medium. The ma jority of the spontaneous mutations (82%) and that of the glyoxal-indu ced mutations (50%) were the addition or deletion of a 5'-TGGC-3' sequ ence at positions 623-634, which was reported to be a mutational hot s pot in the lacI gene. In the glyoxal-induced mutants, however, the rat io of base-pair substitutions was increased (35%). Although all types of base-pair substitutions were detected, 78% of the base-pair substit utions occurred at G:C sites. Among them, G:C --> A:T transitions were predominant, followed by G:C --> T:A transversions, These mutations a ppeared to be distributed randomly within the lad gene. These results suggest that glyoxal-induced mutations may correlate to mutations indu ced by oxygen free-radicals.