Release of snRNP and RNA from transcription sites in adenovirus-infected cells

Small nuclear ribonucleoprotein (snRNP) splicing factors colocalize with nascent RNA in the nucleus of adenovirus-infected cells in a pattern that appears as a series of rings surrounding viral replication centers. We have studied the release of snRNP and RNA from transcription sites following transcription inhibition by actinomycin D. SnRNP, poly(A) RNA, and viral RNA were no longer detected in the ring pattern following transcription inhibition and were instead detected in nuclear clusters. Release of snRNP from transcription sites was blocked when transcription was inhibited at 4 degrees C, suggesting that release requires temperature-dependent processes. Release of snRNP was also inhibited when transcription was blocked in the presence of 9-beta-D-arabinofuranosyladenine, to inhibit 3'-end cleavage and polyadenylation, or staurosporine, to inhibit kinases. By contrast, release of snRNP was not inhibited when transcription was blocked in the presence of cordycepin, to inhibit RNA polyadenylation without affecting 3'-end cleavage, or okadaic acid, to inhibit phosphatase activity. Our results suggest that temperature-dependent processes involved in the release of splicing factors from transcription sites could include 3'-end cleavage of pre-mRNA and phosphorylation events inhibited by stauropsorine.