CRYSTAL STRUCTURE OF UNLIGANDED AZT-RESISTANT HIV-1 REVERSE TRANSCRIPTASE TRANSFERASE, REVERSE TRANSCRIPTASE, AZT RESISTANCE MECHANISM, P51/P66, HETERO DIMER, NUCLEOSIDE INHIBITOR, AIDS, HIV, DNA RECOMBINATION, RNA- DIRECTED DNA POLYMERASE, DNA POLYMERASE, MULTIFUNCTIONAL ENZYME, AZT, AZT RESISTANCE, NRTI, AZT RESISTANCE MUTATIONS 3KLI