Abstract
A family of related cell lines was generated by subcloning of a hamster cell line (ev-1114-CHL-2) that had been transformed by a variant (ev-1114) of Simian Virus 40 (SV40). The viral sequences in these cells were examined using restriction enzymes and Southern-blotting technology. The analysis indicated that the parental conformation of the viral sequences integrated into the cell chromosome had been unstable, giving rise to multiple rearrangements. This instability was inherited by at least one of the subclones. Spontaneous appearance of free viral DNA in the subclones was greatly reduced from parental levels, and, unlike the parent cell line, treatment of the subclones with Mitomycin C or fusion with permissive BSC-1 cells did not rescue substantial quantities of free viral sequences. Successful rescue by fusion to cos-1 cells, which contain an active T-antigen, showed that this phenomenon was probably due to a T-antigen defect.The behaviour of SV40 in semipermissive hamster cells resembles that of polyoma virus as it has been studied in rat cells. Integrated viral genes are unstable and recombine frequently. There seems to be a selective pressure to abolish certain viral gene functions while retaining others, resulting in the evolution of mutant T-antigens.