MOLECULAR ANALYSIS OF THE ORFS 3 TO 7 OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS, QUEBEC REFERENCE STRAIN

The cDNA sequence of the 3'-terminal genomic region of the Quebec IAF-exp91 strain of porcine reproductive and respiratory syndrome virus (PRRSV) was determined and compared to those of other reference strains from Europe (Lelystad virus) and US (ATCC VR2385, MN-lb). The sequence (2834 nucleotides) which encompassed ORFs 3 to 7 revealed extensive genomic variations between the Quebec strain and Lelystad virus (LV)?, resulting from high number of base substitutions, additions and deletions. The ORFs 5, 3, and 7 seemed to be relatively the most variable; the predicted encoding products of the Quebec and LV strains displayed only 52%, 54%, and 59% amino acid identities, respectively. Nevertheless, in vitro translation experiments of the structural genes (ORFs 5, 6, and 7) and radioimmunoprecipitation assays with extracellular virions gave results similar to those previously reported for LV. In contrast, close genomic relationships were demonstrated between Quebec and US strains. Taking together, these results indicate that, although structurally similar, North American PRRSV strains belong to a genotype distinct from that of the LV, thus supporting previous findings that allowed to divide PRRSV isolates into two antigenic subgroups (U.S. and European).