INSERTION OF N-LINKED GLYCOSYLATION SITES IN THE VARIABLE REGIONS OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 SURFACE GLYCOPROTEIN THROUGH AAT TRIPLET REITERATION

Variable regions with sequence length variation in the human immunodeficiency virus type 1 envelope exhibit an unusual pattern of codon usage with AAT, ACT, and AGT together composing >70% of all codons used. We postulate that this distribution is caused by insertion of AAT triplets followed by point mutations and selection. Accumulation of the encoded amino acids (asparagine, serine, and threonine) leads to the creation of new N-linked glycosylation sites, which helps the virus to escape from the immune pressure exerted by virus-neutralizing antibodies.