EFFECTS OF 2ND-SITE MUTATIONS ON DOMINANT INTERFERENCE BY A HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ENVELOPE GLYCOPROTEIN MUTANT

We have demonstrated previously that a human immunodeficiency virus ty pe 1 (HIV-1) envelope glycoprotein containing a Val-to-Glu substitutio n at the second amino acid of the transmembrane glycoprotein gp41 (ter med the 41.2 mutant) dominantly interferes with wild type envelope-med iated syncytium formation and virus infectivity. To understand the mec hanism by which the 41.2 mutant exerts the dominant interfering phenot ype and thereby determine further how the mutant might be used as an i nhibitor of viral spread, additional mutations were made in the envelo pe gene, and the effects of these mutations on interference were deter mined. It was found that processing of the 41.2 mutant glycoprotein to gp120 and gp41 subunits and a functional CD4-binding domain are neces sary for the interfering phenotype to be exhibited fully. However, nei ther a wild-type V3 loop nor the gp41 cytoplasmic tail is necessary fo r efficient interference. In addition, it was determined that the domi nant interfering phenotype is not conferred exclusively by the glutama te substitution at amino acid 2 of gp41, since a substitution with a b asic residue at this position also results in a dominant interfering e nvelope glycoprotein.