HIV-1 RT is an asymmetric heterodimer which is 1000 amino acid long and is composed of two subunits. The larger subunit, p66, is 560 amino acid long and it exhibits all the enzymatic activities of the RT. The smaller subunit, called p51, is 440 amino acid long and it is considered to stabilize the heterodimer but also it may take part in the binding of the tRNA primer.  The p66 subunit has the two active sites: polymerase and ribonuclease H. The polymerase has four subdomains that have been named “fingers“, “thumb“, “connection“ and “palm“ for it has been compared to the right hand.