A big problem with HIV is that, being a retrovirus, it initially copies itself in the reverse of the usual direction. This RNA -> cDNA process requires reverse

A big problem with HIV is that, being a retrovirus, it initially copies itself in the reverse of the usual direction. This RNA -> cDNA process requires reverse transcriptase[1], which is notorious for introducing errors. Even worse, the reverse transcriptase in HIV is particularly bad. Rapidly changing targets are nasty.... [1] http://en.wikipedia.org/wiki/Reverse_transcriptase http://en.wikipedia.org/wiki/Reverse_transcriptase