FIG. 4.

Coreceptor usage of chimeras generated between related env genes with distinct phenotypes. (A) Construction of recombinant env genes. Chimeras were made between the R5X4 89.6 env molecular clone and the R5 variant 14, and between 89.6 and the X4 variant 22. Overlap extension PCR was used to exchange the indicated regions, which introduced the amino acid changes noted. (B) Coreceptor selectivity of chimeric env variants. The env chimeras were tested for CCR5 and CXCR4 utilization based on cell-cell fusion.