Isolation of double lysogens from 3T3 cells transformed by plaque morphology mutants of SV40.

Simian virus 40 (SV40) rescued from 3T3 lines transformed independently by fuzzy plaque strain, SV40 (mKS-U4), and small-clear plaque strain, SV40 (mKS-U88), resembled the virus used to initiate the transformation. When a mixture of the two viruses was used for transformation, both plaque types could be rescued. Two clonal lines, after fusion with CV-1 cells, yielded both plaque types of infectious centers, and a third clonal line, 3T3(4-88)G-1, yielded fuzzy and small-clear plaque types of infectious centers plus large-clear infectious centers resembling "wild-type" SV40 clone 307L. Two secondary and 14 tertiary clones of 3T3(4-88)G-1 were isolated, all of which yielded fuzzy plaque type and clear infectious centers after fusion with CV-1 cells. When these infectious centers were picked and replated on CV-1 cells, the fuzzy and small-clear plaque types of SV40, as well as a large-clear plaque type resembling parental SV40, were isolated.