Since RT dimer is the stable form which remains resistant to the proteolysis, we tested whether treatment of dimerization enhancer could reduce the mutant RT proteolysis. Wild type and mutant pseudoviruses were generated in the presence or absence of Efavirenz (EFV), the most potent dimerization enhancer [26] . The results showed that the RT mutants were still undetectable in the presence of EFV (Fig. 5A) . The conformation of the wild type and mutant RT p66 was further analyzed by native gel electrophoresis followed by Western blotting (Fig. 5B) . Under native conditions, wild type p66 subunit formed homodimer. However, the formation of homodimer in mutant Y271A was markedly reduced and a higher order oligomer appeared, which might be tetramer according to its molecular weight, while mutant I274A existed as at least two higher order oligomers, which were likely tetramer and octamer based on their molecular weights. However, the exact nature of the oligomers formed by mutant p66 subunits remained to be clarified. Furthermore, the treatment with b-mercaptoethanol could partially disrupt the higher order oligomers and improve dimer formation. This result implicated that dimer formation might be necessary for the stability of RT and its resistance to proteolysis after incorporation of Gag-Pol polyprotein into the viral particles.