SEQUENCE-ANALYSIS OF OPEN READING FRAMES (ORFS) 2 TO 4 OF A US ISOLATE OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS - BRIEF REPORT

The sequence of ORFs 2 to 4 of a U.S. isolate of porcine reproductive and respiratory syndrome virus (PRRSV), ATCC VR2385, was determined by analysis of a cDNA lambda library. The cDNA clones containing PRRSV s pecific sequences were selected using a VR2385 ORF 4 specific PCR prob e and sequenced. The ORFs 2, 3 and 4 overlapped each other and encoded polypeptides with predicted M(r) of 29.5 kDa (ORF 2), 28.7 kDa (ORF 3 ) and 19.5 kDa (ORF 4), respectively. No overlap was found between ORF s 4 and 5, and instead there was a 10 bp sequence which separated thes e two ORFs. The nucleic acid homology with corresponding ORFs of the E uropean PRRSV isolate Lelystad virus (LV) was 65% for ORF 2, 64% for O RF 3 and 66% for ORF 4. Comparison of the ORF 4 sequences of VR2385 wi th that of another U.S. isolate MN-lb revealed only 86% amino acid seq uence homology and the presence of deletions in the ORF 4 of MN-lb. Ou r results further strengthen the observation that there is sequence va riation between US and European PRRSV isolates.