Comparisons of the Pestivirus Bovine Viral Diarrhoea Virus with Members of the Flaviviridae

The molecular features of bovine viral diarrhoea virus (BVDV), a member of the Pestivirus genus currently classified in the Togaviridae, were examined for characteristics resembling those of the Flaviviridae family. Like flaviviruses, BVDV possesses a single-stranded RNA genome (approx. 4.3 x 10(6) Mr) deficient in a 3' poly(A) tract. This RNA has a single open reading frame spanning the length of the genome in the viral RNA sense (positive polarity), implying an expression strategy involving the processing of a precursor polyprotein. With the exception of several short but significant stretches of identical amino acids within two non-structural proteins, no extended regions of nucleotide or amino acid sequence homology between BVDV and representatives of three serological subgroups of mosquito-borne flaviviruses were noted. However, comparison of the organization of protein-coding domains along the genomes and the hydropathic profiles of amino acid sequences revealed pronounced similarities. It is proposed that Pestivirus, of which BVDV is the prototype member, should no longer be grouped in the Togaviridae family, but rather be considered a genus of non-arthropod-borne viruses within the Flaviviridae.