Expression of the autonomous parvovirus H1 genome: evidence for a single transcriptional unit and multiple spliced polyadenylated transcripts.

We identified viral transcripts in parvovirus H1-infected rodent cells using the S1 nuclease mapping technique of Berk and Sharp (1977, 1978). The most abundant viral transcript, present in both nucleus and cytoplasm, is approximately 2.8 kb long and represents about 56% of the viral genome. Less abundant viral transcripts of 3.0, 1.45 and 1.30 kb, and possibly other minor viral transcripts, are also detected in nuclear and cytoplasmic fractions. In contrast, a prominent 4.7 kb viral transcript which corresponds to 95% of the viral DNA is found only in the nucleus; this finding suggests that the parvovirus genome may function as a single transcription unit. Virus-infected cells pretreated with cycloheximide accumulate all these viral transcripts. Analyses of RNA-DNA hybrids (isolated from neutral agarose gels) by electrophoresis on alkaline agarose gels indicate that the 4.7, 3.0 and 2.8 kb viral transcripts are "spliced" RNAs. The nuclear-specific 4.7 kb transcript appears to be encoded by two noncontiguous DNA segments of 2.2 and 2.6 kb. The 3.0 and 2.8 kb transcripts are apparently encoded by.a 2.6 kb segment of DNA and one or more much smaller noncontiguous DNA segments, one of which is approximately 170 nucleotides long.