TRANSCRIPTIONAL MAPPING OF THE 3' END OF THE BOVINE SYNCYTIAL VIRUS GENOME

The bovine syncytial virus, a member of the retroviral subfamily Spuma virinae, causes a persistent, asymptomatic infection in cattle. Nucleo tide sequence analysis of the viral genome revealed two overlapping re ading frames in the 3' region, traditionally occupied by accessory-fun ction genes in other complex retroviruses. In order to analyze the tra nscripts from the accessory-gene region, we designed oligonucleotide p rimers complementary to sequences within the 5' and 3' long terminal r epeats (LTRs) for use with the PCR. Southern blot analysis of amplific ation products revealed eight major cDNA bands. Eleven distinct cDNA c lones were subsequently isolated and characterized. The initial splice donor in each clone is located 49 bp downstream from the mRNA cap sit e in the 5' LTR. The primary splice acceptor site was located 17 bp up stream from the proximal 3' open reading frame known as BF-ORF1. A sec ond major splice acceptor was localized to a region upstream of the se cond open reading frame, BF-ORF2. Clones were identified which spliced directly to each of these sites. Additional splice donor and acceptor sites within BF-ORF1 and BF-ORF2 and the 3' LTR were variously used t o generate a complex array of multiply spliced transcripts. Each of th ese transcripts remained in frame and coded for a potential protein pr oduct.