c-Ha-ras containing 8-hydroxyguanine at codon 12 induces point mutations at the modified and adjacent positions

To determine the type of mutation induced by 8-hydroxyguanine in a mammalian system, we examined the mutations induced by a synthetic c-Ha-ras protooncogene containing 8-hydroxyguanine in the second position of codon 12 (GGC) in NIH3T3 cells. Transfection of this gene significantly increased the number of transformed foci. The c-Ha-ras gene present in these foci was analyzed by the polymerase chain reaction-restriction enzyme method. Interestingly, sequence analysis revealed random mutations at the modified site (G----T, G----A, and G----C) as well as mutations of the adjacent G on the 5'-side of 8-hydroxyguanine (G----A and G----T).