Crosslinking of substrates occurs exclusively to the p66 subunit of heterodimeric HIV-1 reverse transcriptase.

Photoaffinity labeling of the hetero- and homodimeric forms of HIV-1 reverse transcriptase has been carried out using [32P]rA12-18.dT10 as a representative template-primer and [alpha-32P]dTTP as a representative 2'-deoxynucleoside-5'-triphosphate. UV irradiation produces stable, covalent crosslinks between each of the reactants and both the hetero-(p66/p51) and homodimeric (p66/p66, p51/p51) forms of the enzyme. In the case of the p66/p51 heterodimer, the form of the enzyme believed to be involved in viral replication, crosslinking occurs exclusively to the p66 subunit. These results suggest that the polymerase activity of the heterodimer residues on p66.