The control of SV40 transcription during a lytic infection: late RNA synthesis in the presence of inhibitors of DNA replication.

The transition from early to late transcription of SV40 DNA in productively infected BSC-1 cells was analyzed using both inhibitors of DNA replication, and early (Group A) temperature sensitive (ts) mutants of SV40. Late virus specific cytoplasmic RNA sedimenting at 16S in neutral sucrose gradients and complementary to the plus (L) DNA strand of SV40 was detected in cultures infected in the presence of three inhibitors of DNA replication (Ara-C, FdU, and chloroquine), even though the inhibition of viral DNA replication appeared to be essentially complete. After infection with the early SV40 mutant tsA58, no DNA replication was detected at the restrictive temperature (41 degrees C) and no significant late RNA complementary to the plus (L) strand was found, in either the cytoplasm or nuclei of infected cells. These data support the concept that expression of late viral functions requires the initiation of viral DNA synthesis or a functional gene A protein, or both.