The regulation of SV40 gene expression in nonpermissive cells

The limitations to SV40 growth in nonpermissive cells are poorly understood. In differentiated mouse cells, early mRNA and T-antigens are synthesized, but no viral DNA replication has been detected. A plausible explanation for the limitation to viral DNA synthesis in these cells might be the inability of a mouse cell-specific DNA polymerase to interact with the SV40 T-antigen-viral DNA complex. In spite of this abortive viral-cell interaction, SV40 late viral transcripts can be detected in infected mouse cells. Both early and late transcripts can be detected in infected mouse cells. Both early and late SV40 transcriptional activities peak between 10 and 15 h post infection; by 24 h after infection SV40 RNA is almost undetectable. In spite of the detection of late SV40 mRNA in mouse cells, we have been unable to detect any structural proteins (VP1, VP2, or VP3) encoded by these transcripts. A more restrictive interaction occurs between SV40 and undifferentiated mouse teratocarcinoma cell lines. Using an in vitro technique, the viral transcriptional complex (VTC) assay, we were able to demonstrate viral transcriptional activity on both the early and the late strands of SV40 in F9 embryonal carcinoma cells. Nevertheless, no mature processed mRNAs or viral encoded polypeptides were detected in these cells. After differentiation of the F9 cells with retinoic acid, however, spliced early mRNAs, as well as the SV40 T-antigen, were present.