Presence of Point Mutations in the N-ras Gene in Radiation-transformed Rat Embryo Cells1

We study the transforming ability of X-rays in multistep carcinogenesis by irradiating primary rat cells which contain transfected c-myc oncogene. X-irradiation induces fully transformed phenotypes, including anchorageindependent growth and tumor formation in nude mice. Of seven foci examined, five exhibited an A to G conversion in codon 61 of the \-nis oncogene. Another transformed isolate has a single G to A base substitu tion in codon 14 in the same oncogene, while no point mutation is detected in the other focus. This is the first in vitro demonstration of the association between point mutation and X-ray-transformed cells.