[Identification of porcine reproductive and respiratory syndrome virus regulation sequence in 3'-untranslated region].

Based on our established infectious clone of PRRSV, designated as pCBC2, a series of mutagenesis of 3'-untranslated region (3'-UTR) at primary structure and secondary structure level were constructed. Then the full length mutant clones were transfected into MARC-145 cells, from which the influences of the discrete 3'-UTR mutation on PRRSV replication and transcription were analyzed. The properties of the rescued mutant viruses were then further characterized by Northern Blot and plaque morphology analysis. Our results demonstrated that PRRSV could tolerate more than 41 nucleotides deletion and 23nt insertion in the 3'-UTR, however, minor changes in the conserved stem loop region destroyed virus infectivity. To sum up, the stem-loop structure was essential for virus viability, but 5' end of the 3'-UTR tolerates certain level of nucleotide deletion or insertion. This is the first report to define the essential sequence and secondary structure for PRRSV genome replication and it is useful for future research about the regulation element.