Structural gene analysis of a Quebec reference strain or porcine reproductive and respiratory syndrome virus (PRRSV)

The 3' end genomic region of a Québec PRRSV reference strain (IAF-exp91), propagated in porcine alveolar macrophages (PAM), was sequenced and compared to the prototype European strain, the Lelystad virus (LV). The sequence, which represents the 3'-terminal 2834 nucleotides, encompassed 5 ORFs corresponding to ORFs 3 to 7 of LV. Extensive genomic variations resulting from an important rate of nucleotide additions, substitutions, and deletions were demonstrated between the two viruses. Indeed, the two corresponding sequences displayed a total of 66% and 63% identity at the nucleotide and amino acid levels, respectively. The predicted products of ORFs 5, 3, and 7, showed the highest rate of amino acid variations with percentages of identity of 52, 54, and 59, respectively. Sequence analysis of an additional Québec strain that could be propagated in a continuous cell line (MARC-145), suggested that Québec PRRSV strains belong to a genotype distinct from that of LV, thus confirming previous serological results which allowed to divide PRRSV isolates into two distinct antigenic subgroups (U.S. and European). Six viral major polypeptides with apparent M(rs) of 14.5K, 15K, 19K, 24.5K, 29K, and 42K could be identified from lysates of viral infected cells, of which the 15, 19 and 24.5K species seemed to be structural. In vitro translation products of ORFs 7 and 6 comigrated with the 15 and 19 K viral proteins, whereas that of ORF 5 may be associated to the 24.5K when translated in presence of microsomes. Consequently, it is likely that ORFs 7 to 5, encode the three major structural proteins.