Natural recombination in bovine viral diarrhea viruses.

BVDV isolates exist as two biotypes differentiated at the molecular level by production of a p80 polypeptide. Insertions consisting of host cell sequences and/or duplicated and rearranged viral sequences have been observed in the portion of the genome coding for the p80 polypeptide in some, but not all, cytopathic BVDV. The significance of these insertions to biotypic expression has yet to be demonstrated. It has been hypothesized that recombination results in the production of the p80 polypeptide by introduction of a cleavage site into a precursor polypeptide or the introduction of a second copy of the p80 gene. Because inserts have not been identified in all cytopathic BVDV examined, it appears that recombination may not be the only mechanism involved in biotypic determination.