Positions of the p51↓RNH cleavage site and the residue T477 in HIV-1 RT. Ribbon diagram of amino acid residues 425-560 depicting the RNH domain of HIV-1 RT, adapted from PDB 1LDO. The H-bond between the hydroxyl of T477 and the main chain of A445 is indicated by a dashed line. Details are provided in the text. The molecular graphics image was produced using the UCSF Chimera package from the resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco (supported by NIH P41 RR-01081) .