Mutations at position 184 of human immunodeficiency virus type-1 reverse transcriptase affect virus titer and viral DNA synthesis.

Methionine at position 184 of human immunodeficiency virus type-1 (HIV-1) reverse transcriptase (RT) was changed to valine, isoleucine, threonine, or alanine in an HIV-1-based vector. The vectors were analyzed for replication capacity and for resistance to the nucleoside analog 2',3'-dideoxy-3'thiacytidine (3TC) using a single-cycle assay. Viruses containing the valine or isoleucine mutations were highly resistant to 3TC and replicated almost as well as the wild-type virus. The virus containing the threonine mutation was resistant to 3TC, but replicated about 30% as well as the wild-type. The alanine mutation conferred partial resistance to 3TC, but replicated poorly. The amounts of viral DNA synthesized decreased in 3TC-treated cells when the cells were infected with wild-type virus and the M184A mutant. The effect of these mutations on the generation of the ends of the linear viral DNA was determined using the sequence of the 2-LTR circle junctions. The M184T mutation increased the proportion of 2-LTR circle junctions containing a tRNA insertion, suggesting that the mutation affected the RNase H activity of RT.