NATURAL RECOMBINATION IN BOVINE VIRAL DIARRHEA VIRUSES

BVDV isolates exist as two biotypes differentiated at the molecular le vel by production of a p80 polypeptide. Insertions consisting of host cell sequences and/or duplicated and rearranged viral sequences have b een observed in the portion of the genome coding for the p80 polypepti de in some, but not all, cytopathic BVDV. The significance of these in sertions to biotypic expression has yet to be demonstrated. It has bee n hypothesized that recombination results in the production of the p80 polypeptide by introduction of a cleavage site into a precursor polyp eptide or the introduction of a second copy of the p80 gene. Because i nserts have not been identified in all cytopathic BVDV examined, it ap pears that recombination may not be the only mechanism involved in bio typic determination.