Expression of 100,000-Mr simian virus 40 (SV40) tumor antigen in mouse fibroblasts transfected with...

Simian virus 40 early region mutants which are partially or completely replication defective were tested for their ability to transform postcrisis mouse fibroblasts. All mutants tested were capable of generating anchorage-independent transformants. We have previously reported the presence of a variant tumor antigen of 100,000 Mr (100K protein) generated upon transformation by wild-type simian virus 40 virions which correlates with anchorage-independent growth (Chen et al., Mol. Cell. Biol. 1:994-1006, 1981). In this study, none of the mutants tested produced the 100K variant protein at early (before the fifth) passage. Long-term passage (greater than 20 weeks) permitted the expression of this 100K variant in half of the transformants. Thus the phenotype of these mutants is different from both wild-type simian virus 40 (frequently production of 100K by the third passage, and always by the tenth passage) and the origin-minus class of mutants (no production of 100K at any passage).