Properties of T antigen-positive phenotypic revertants isolated from SV40-transformed rat and mouse cells

Four T antigen-positive phenotypic revertants were isolated by negative selection with BUdR from SV40-transformed rat and mouse cells which contain six and two viral genome equivalents per cell, respectively. Karyological analysis indicated that one rat and one mouse revertant had a hyperploid number of chromosomes, while the remaining two rat revertants had a subtetraploid number similar to those of the transformed parent cells. The hyperploid revertants were unable to grow in soft agar medium and were nontumorigenic in nude mice. One of the subtetraploid revertants formed large colonies at a very low frequency and induced tumors after a prolonged incubation period. These results indicate that there is a good correlation between the capacity of cells to grow without anchorage and the capacity to form tumors in nude mice and suggest that the revertant phenotype is stable in the presence of T antigen when the number of chromosomes is greatly increased as compared with that of the transformed parent cells.