The simian virus 40 sequences between 0.169 and 0.423 map units are not essential to immortalize early-passage rat embryo cells.

F8dl is a simian virus 40 early-region deletion mutant that lacks the sequences between 0.169 and 0.423 map units. We show that cloned F8dl DNA immortalized early-passage Fisher rat embryo cells with an efficiency that was about 20% of that of cloned wild-type simian virus 40 DNA. In contrast, we detected no immortalized colonies when we transfected the cells with DNA of five other early-region deletion mutants that do not make stable truncated forms of T antigen. Since all five of these mutants have intact early- and late-region control sequences, we conclude that these control sequences are not sufficient for immortalization. Three of the mutants that did not immortalize did make a normal small t antigen, suggesting that the expression of this protein alone is not sufficient for immortalization of early-passage Fisher rat embryo cells.