Molecular characterization of PL97-1, the first Korean isolate of the porcine reproductive and respiratory syndrome virus

We determined the complete nucleotide and predicted amino acid sequence of the genomic RNA of PL97-1, the first Korean strain of porcine reproductive and respiratory syndrome virus (PRRSV), which was isolated from the serum of an infected pig in 1997. We found that the 15411-nucleotide genome of PL97-1 consisted of a 189-nucleotide 5' noncoding region (NCR), a 15071-nucleotide protein-coding region, and a 151-nucleotide 3'NCR, followed by a poly (A) tail. The 5'-end of PL97-1 began with 1ATG ACG TAT AGG12. Comparison of the PL97-1 genome with the 11 fully sequenced PRRSV genomes currently available revealed sequence divergence ranging from 0.3% (the VR-2332-derived vaccine MLV RespPRRS/Repro strain) to 38% (the Dutch Lelystad strain). To better understand the genetic relationships between these different strains, phylogenetic analyses were performed on the full-length PRRSV genomes. Significantly, the phylogenetic tree based on the ORF1b or ORF7 genes most closely resembled the tree based on the full-length genomes. Thus, these single genes will be the most useful in revealing the genetic relationships between the different strains relative to their geographical distribution. Extensive phylogenetic analyses using the ORF7 sequences of 111 PRRSV isolates available revealed that PL97-1 is most closely related to the North American genotype VR-2332, a VR-2332-derived vaccine strain, and Chinese BJ-4. It is distantly related to the European genotype Lelystad. This study provides the largest full-length genome phylogenetic analysis of PRRSV that has been published to date, and supports an earlier genetic grouping of the many temporally and geographically diverse PRRSV strains currently isolated.