SIZE VARIATION WITHIN THE 2ND HYPERVARIABLE REGION OF THE SURFACE ENVELOPE GENE OF THE BOVINE LENTIVIRUS BIV IN EXPERIMENTALLY AND NATURALLY INFECTED CATTLE

The bovine lentivirus also known as the bovine immunodeficiency-like v irus (BIV) has conserved and hypervariable regions in the surface enve lope (SU) gene. Size variation between isolates can be as large as 200 bp, mostly occurring in the second hypervariable (V2) gene region of the SU gene. The V2 region was cloned and sequenced from both experime ntally and naturally infected cattle. Temporal evaluation of provirus from an experimentally inoculated cow showed two different-sized varia nts that appeared over time. The variation appeared to result from a r ecombinational event resulting in an apparent direct repeat. Cloned pr oviral nucleotide sequence diversity increased over time. Virus that w as cultured and then cloned and sequenced showed progressive change fr om the inoculum virus, but culturing reduced the diversity of the clon es as compared with direct amplification of provirus from leukocyte sa mples from the cow. The quasispecies phenomenon was evident in clones sequenced from a cow naturally infected with BIV. Of 10 clones examine d from the V2 region, 6 different-size clones were present with nine d ifferent patterns of sequence rearrangement. Sequence length of differ ent clones varied by as much as 43 amino acids (aa), with 21- and 15-a a direct repeats accounting for most of the size variation. Similar to other lentiviruses, BIV appears to mutate rapidly, which may be impor tant in viral persistence and pathogenesis.