Probing the sequence space available for HIV-1 evolution.

We designed a novel experimental approach to probe the sequence space available for HIV-1 evolution. Selective pressure was put on conserved HIV-1 genomic sequences by means of RNA interference (RNAi). Virus escape was monitored in many parallel cultures, and we scored the mutations selected in the RNAi target sequences. The experimentally induced sequence variation closely resembles the sequence variation of natural HIV-1 strains. This indicates that we actually mapped a restricted area of sequence space compatible with virus replication.