FIG. 2.

Phylogenetic tree analysis. Neighbor-joining trees were created with the full length gag (a) and pol (b) genes of HIV-1 sequences from the intravenous drug use (IDU) population in Liangshan prefecture and a selection of reference sequences of subtype A–D, F–H, J, K, CRF01_AE, CRF07_BC, and CRF08_BC (black dots, http://hiv-web.lanl. gov/). The lengths of the gag and pol genes of HIV-1 sequences obtained in the study were 1,503 and 3,056 base pairs using HXB2 as the genomic calibrator. Each reference sequence is labeled with the HIV-1 subtype, followed by the sequence name. The bootstrap values supporting the branch (more than 70%) are indicated at the corresponding nodes of the tree. The scale bars representing genetic distances are listed below.