SHORT COMMUNICATION Mutagenesis of H-ras codons 11 and 12 in human fibroblasts by iV-ethyl-./V-nitrosourea

Codon 12 of the ras protooncogenes represents a mutational hotspot in human cancer. A distinct pattern of base pah-changes has been observed that may allow insight into the class of carcinogens that induced the mutations. In an attempt to identify candidate carcinogens we have studied the mutability of codons 11 (GCQ and 12 (GGC) of the c-H-rasl gene hi human foreskin fibroblasts to iV-ethyl-iV-nitrosourea (ENU) by restriction fragment length polymorphism/polymerase chain reaction (RFLP/PCR). This genotypic mutation system allows the quantHation of low frequencies of mutated sequences without expansion and phenotypic selection of mutated cells. ENU induced the transition of G to A in the middle position of codon 12 with highest efficiency. This is the same mutation that is found predominantly in human tumors. These mutations are most likely the consequence o