Isolation of cellular revertants from a rat cell line transformed by the E6 and E7 genes of human papillomavirus type 16.

Three revertants defective in the ability to form colonies in semisolid medium were isolated from a rat cell line transformed by the E6 and E7 genes of human papillomavirus type 16 (HPV16). These revertants appeared to be defective in a cellular factor(s) necessary for transformation by HPV16-E6E7 genes since they still expressed a comparable amount of HPV16-E6E7 mRNA and E7 protein to the parental cells, harbored rescuable transforming virus, and were resistant to retransformation by HPV16-E6E7 genes. All these reverted phenotypes of the three mutants were recessive on somatic cell hybridization with normal cells, because all the hybrids showed transformed phenotypes.