The RNA genome of HIV-1, like that of other retroviruses, is reverse-transcribed (Baltimore 1970; Temin and Mizutani 1970) into double-stranded DNA, which is then integrated into a host cell chromosome and transcribed to yield both viral mRNAs and viral genomic RNAs. HIV-1 reverse transcription takes place in the cytosol of a newly infected host cell and involves multiple steps of RNA synthesis and degradation of the RNA strand of RNA:DNA duplexes mediated by the HIV-1 RT protein, as well as two template switches, to yield a DNA duplex colinear with the viral genomic RNA but with additional Long Terminal Repeat (LTR) sequence motifs at both ends (Telesnitsky and Goff 1997; Jonckheere et al. 2000).
HIV-1 RT has two catalytic activities essential for transcription of a DNA duplex copy of the viral genomic RNA: a reverse transcriptase activity and an RNase H activity. The reverse transcriptase is primer dependent and can transcribe both RNA and DNA templates in a 5'-3' direction. The RNaseH acts on the RNA strand of RNA:DNA duplexes and can catalyze both endo- and exonucleolytic cleavage of such an RNA strand. RT is a heterodimer of 66 and 51 kD polypeptides, both generated by cleavage of the HIV-1 Pol gene product: p66 contains Pol amino acid residues 599-1158; p51 contains residues 599-1038. Both active sites of the HIV-1 RT enzyme are contained in the p66 polypeptide, the polymerase activity in its aminoterminal region, and the RNase in its carboxyterminus. The p51 subunit lacks an RNaseH domain, and while its polymerase domain is intact, its conformation in the p66:p51 heterodimer occludes the active site (Hughes et al. 1996; Jacobo-Molina et al. 1993; Kohlstaedt et al. 1992; Wang et al. 1994).
The process of reverse transcription is outlined in the figure below: viral genomic RNA and primer tRNA are shown in black, "minus" strand DNA is shown in red, and "plus" strand DNA is shown in blue.