Structures of reverse transcriptase pre- and post-excision complexes shed new light on HIV-1 AZT resistance.

HIV-1 resistance to 3'-azido-2',3'-deoxythymidine (AZT, zidovudine) results from mutations in reverse transcriptase that increase the ability of the enzyme to excise AZT-monophosphate after it has been incorporated. Crystal structures of complexes of wild type and mutant reverse transcriptase with double-stranded DNA with or without the excision product, AZT adenosine dinucleoside tetraphosphate (AZTppppA), have recently been reported. The excision-enhancing mutations dramatically change the way the enzyme interacts with the excision product.