Immortalization of rodent embryo fibroblasts by SV40 is maintained by the A gene

SV40 can induce proliferation of primary cells from various origins and by making them escape from senescence confer a potential of unlimited division characteristic of established cell lines. We have studied this effect called immortalization with various mutants of the SV40 early genes. The results establish that the immortalized phenotype is controlled by the A gene in a reversible fashion. Cells immortalized at 33 degrees by a tsA mutant, revert to a "mortal" or senescent-like phenotype after temperature shift up to 39 degrees. The nature of these striking phenotypic changes is discussed.