Replacement of the heterologous 5′ untranslated region allows preservation of the fully functional activities of type 2 porcine reproductive and respiratory syndrome virus

The 5′ untranslated region (UTR) is believed to be vital for the replication of porcine reproductive and respiratory syndrome virus (PRRSV), yet its functional mechanism remains largely unknown. In this study, to define the cis-acting elements for viral replication and infectivity, The 5′ UTR swapping chimeric clones pTLV8 and pSHSP5 were constructed based on two different genotypes full-length infectious cDNA clone pAPRRS and pSHE backbones. Between them, vTLV8 could be rescued from pTLV8 and had similar virological properties to vAPRRS, including phenotypic characteristic and RNA synthesis level. However, pSHSP5 exhibited no evidence of infectivity. Taken together, the results presented here demonstrate that only the 5′ UTR of type 1 PRRSV did not affect the infectivity and replication of type 2 PRRSV in vitro. The 5′ UTR of type 2 PRRSV could be functionally replaced by its counterpart from type 1.

► The 5′ UTR of inter-genotypic swapping mutation have different consequences of viral rescue, RNA synthesis and protein expression.
► Replacement of the type 1 5′ UTR allows preservation of the fully functional activities of type 2 PRRSV, while converse substitution cause chimera lethal.
► The virological properties and RNA synthesis level of vTLV8 are almost indistinguishable from those of the parental virus.
► Type 1 5′ UTR chimeric virus vTLV8 is genetically stable and possesses nucleotides mutations in the nsp9 region.