Abstract
In contrast to most gammaretrovirus envelope proteins (Env), the Gibbon ape leukemia virus (GaLV) Env protein does not mediate the infectivity of human immunodeficiency virus type 1 (HIV-1) particles. We made use of this observation to set up a directed evolution system by creating a library of GaLV Env variants diversified at three critical amino acids, all located around the R-peptide cleavage site within the cytoplasmic tail. This library was screened for variants that were able to functionally pseudotype HIV-1 vector particles. All selected Env variants mediated the infectivity of HIV-1 vector particles and encoded novel cytoplasmic tail motifs. They were efficiently incorporated into HIV particles, and the R peptide was processed by the HIV protease. Interestingly, in some of the selected variants, the R-peptide cleavage site had shifted closer to the C terminus. These data demonstrate a valuable approach for the engineering of chimeric viruses and vector particles.