Homodimeric reverse transcriptases from rous sarcoma virus mutated within the polymerase or RNase H active site of one subunit are active.

Heterodimeric reverse transcriptase (RT) alphabeta from Rous sarcoma virus (RSV) possesses an asymmetric subunit organization with the polymerase and RNase H active sites localized in the alpha subunit. To determine whether homodimeric RSV RTs alpha (63 kDa) or beta (95 kDa) assume alpha subunit organization similar to that of the heterodimer, an essential aspartic acid residue was mutated in the active site of either the polymerase (Asp181 > Asn) or the RNase H (Asp505 > Asn). Homodimeric alpha or beta RT consisting of one wild-type and one mutated subunit exhibit polymerase or RNase H activity, respectively, whereas the corresponding doubly mutated enzymes are inactive, indicating that the catalytic sites of the polymerase and RNase H domains are formed by only one subunit of the homodimer.