Precise mapping of recombination breakpoints suggests a common parent of two BC recombinant HIV type 1 strains circulating in China.

Two different BC recombinant HIV-1 strains have arisen and begun to circulate among intravenous drug users in China. The recombinants are mostly subtype C with a few small subtype B segments. Additional full-genome sequences of the two recombinants, termed CRF07_BC and CRFO&_BC, are now available for analysis. Four CRF07_BC strains, including c54, 97CNU01, 98CN009, and a new strain CNGL-179, described here, and four CRF08_BC strains, including 97CNGX-6, 97CNGX-7, 97CNGX-9, and 98CN006, were compared for their recombination breakpoints by bootscanning and software for fine mapping of recombinants. The four CRF07_BC strains shared an identical recombination structure and the four CRF08_BC strains shared an identical, but different, recombination structure. The two CRFs share five precise subtype B/C boundaries, although although other segments differ between them, suggesting that they shared a common ancestor, itself a BC recombinant that separately "back-crossed" onto different subtype C strains. Both CRFs are broadly distributed from north to south in western China and have maintained low interpatient diversity.