Molecular cloning of biologically active proviruses of bovine immunodeficiency-like virus.

A series of independent proviral molecular clones of bovine immunodeficiency-like virus (BIV) obtained from a genomic library of BIV-infected bovine cell DNA were physically and biologically characterized. Heteroduplex mapping shows that two of these BIV clones (106 and 127) contain uninterrupted proviral sequences approximately 9.0 kb in length, flanked by nonhomologous bovine cellular sequences. Microinjection of purified DNA from BIV clone 106 or 127 into susceptible bovine cells produces virus-specific cytopathic effects, including syncytium induction, supernatant reverse transcriptase activity, and infectious virus particle formation, similar to the effects produced by parental virus stock. Using restriction enzyme mapping, it was determined that the two infectious clones share 13 of 14 sites mapped within the provirus; thus, based on this criterion, the two clones are nearly identical, with the exception of a single polymorphic site recognized in the 3' half of the genome. BIV appears to be an exogenous pathogenic virus, because Southern hybridization analyses detected no endogenous sequences related to BIV in DNA from a variety of uninfected bovine cells and tissues. Most of the BIV-related DNA found in cells 96 hr after infection is present as linear unintegrated viral DNA, although the presence of host flanking sequences in our proviral clones indicates that integration takes place. These biologically active clones of BIV will be of use in defining further the mechanisms of BIV pathogenesis and in engineering specific diagnostic reagents to determine the prevalence of BIV in cattle populations.