New chimeric splice junction in adenovirus type 2-simian virus 40 hybrid viral mRNA.

We have examined hybrid viral RNAs synthesized in both human and monkey cells infected by three nondefective adenovirus type 2 (Ad2)-simian virus 40 (SV40) hybrid viruses; Ad2+ND1, Ad2+ND2, and Ad2+ND4. Most of the hybrid viral RNA molecules appeared to be initiated within adenoviral sequences, but were polyadenylated on their 3' end at the early SV40 mRNA polyadenylation site. The Ad2+ND4 stock of virus was not homogeneous, but consisted of two principle populations of viral DNA. Both populations contained a segment of SV40 DNA extending from the SV40 map positions 0.63 to 0.11 in a left-to-right orientation at adenovirus map position 0.82. One population contained an intact SV40 segment, whereas the other (representing 80 to 85% of the population) has a 500-base pair deletion mapping from approximately 0.60 to 0.50 SV40 map units. This deletion encompassed the SV40 DNA segment which encodes the early SV40 splice sites. Cells infected by the mixed Ad2+ND4 population induced the synthesis of at least three major SV40 RNA species among the hybrid viral transcripts. The most abundant of these hybrid mRNA's appeared only late in the lytic cycle, after the onset of viral DNA replication. It contained an RNA splice junction which extended from a donor (5') nucleotide within the adenoviral RNA sequences to an acceptor (3') splice site within the early region of SV40 at 0.46 SV40 map units. This SV40 acceptor splice site was remarkable in that its use has not been detected in the spliced viral mRNA's of SV40-infected or -transformed cells.