Simian immunodeficiency virus (SIVmac) exhibits complex splicing for tat, rev, and env mRNA

The simian immunodeficiency virus (SIV) is a T-lymphotropic lentivirus associated with a fatal AIDS-like disease in rhesus macaques. SIV has a complex genome encoding virion structural proteins, transactivators, and accessory genes. From lymphoid cells chronically infected with a biologically active molecular clone of SIV, SIVmac1A11, the polymerase chain reaction technique has been used to selectively amplify transcripts for viral transactivators and the envelope gene. Three species of mRNA encoding only rev, and three mRNA encoding both rev and tat were identified by nucleotide sequence analysis. They differed in the splice acceptor sites utilized upstream of the first coding exon, in the presence or the absence of noncoding exons between the major splice donor at the LTR and the splice acceptor at the first coding exons, and in the splicing pattern between the coding exons. Alternate splice acceptors were utilized between the coding exons of tat and rev, but the altered tat proteins did not differ in their ability to transactivate the SIV-LTR. The splicing for env mRNA is more complex than previously reported. Both singly and multiply spliced transcripts exist for env mRNA, and the same splice acceptor site is utilized by both rev and env mRNA.