Functional comparison of transactivation by simian immunodeficiency virus from rhesus macaques and human immunodeficiency virus type 1.
Simian immunodeficiency virus from rhesus macaques (SIVmac), like human immunodeficiency virus type 1 (HIV-1), encodes a transactivator (tat) which stimulates long terminal repeat (LTR)-directed gene expression. We performed cotransfection assays of SIVmac and HIV-1 tat constructs with LTR-CAT reporter plasmids. The primary effect of transactivation for both SIVmac and HIV-1 is an increase in LTR-directed mRNA accumulation. The SIVmac tat gene product partially transactivates an HIV-1 LTR, whereas the HIV-1 tat gene product fully transactivates an SIVmac LTR. Significant transactivation is achieved by the product of coding exon 1 of the HIV-1 tat gene; however, inclusion of coding exon 2 results in a further increase in mRNA accumulation. In contrast, coding exon 2 of the SIVmac tat gene is required for significant transactivation. These results imply that the tat proteins of SIVmac and HIV-1 are functionally similar but not interchangeable. In addition, an in vitro-generated mutation in SIVmac tat disrupts splicing at the normal splice acceptor site at the beginning of coding exon 2 and activates a site approximately 15 nucleotides downstream. The product of this splice variant stimulates LTR-directed gene expression. This alternative splice acceptor site is also used by a biologically active provirus with an efficiency of approximately 5% compared with the upstream site. These data suggest that a novel tat protein is encoded during the course of viral infection.
Viglianti
G A
GA
Department of Cancer Biology, Harvard School of Public Health, Boston, Massachusetts 02115.
Mullins
J I
JI
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004279:DNA, Viral / Q000235:genetics; D004720:Endonucleases; D005091:Exons; D005786:Gene Expression Regulation; D015696:Gene Products, tat; D015497:HIV-1 / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D008253:Macaca mulatta; D008969:Molecular Sequence Data; D010957:Plasmids; D012326:RNA Splicing; D012333:RNA, Messenger / Q000096:biosynthesis; D015302:Simian Immunodeficiency Virus / Q000235:genetics*; D015719:Single-Strand Specific DNA and RNA Endonucleases; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D014162:Transfection; D054322:tat Gene Products, Human Immunodeficiency Virus
D004279:DNA, Viral; D015696:Gene Products, tat; D012333:RNA, Messenger; D014157:Transcription Factors; D054322:tat Gene Products, Human Immunodeficiency Virus; D004720:Endonucleases; D015719:Single-Strand Specific DNA and RNA Endonucleases