College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, PR China.
Virus Res. 2013 Jan;171(1):178-85. doi: 10.1016/j.virusres.2012.11.005. Epub 2012 Dec 5.
It has been shown that ORF5a protein in EAV is important but not essential for virus infectivity. In this study, we found that RNA changes in the overlapping region (1-104 nucleotide, nt) between ORF5 and ORF5a introduced by codon-optimized GP5 was lethal for virus viability, suggesting that the nt changes or amino acid (aa) mutations in the GP5 or ORF5a protein did not permit the production of infectious virus. Furthermore, inactivation of ORF5a expression in the context of type 1 (pSHE) and type 2 (pAJXM and pAPRRS) full-length PRRSV cDNA clones was lethal for the production of infectious virus, while viable PRRSV could be recovered by expressing ORF5a protein in trans, suggesting that ORF5a protein was essential for virus viability. Finally, ORF5a protein could be putatively extended to 63 aas by inactivation of the downstream stop codon candidates, thereby demonstrating that the C-terminus of ORF5a may be variable.
已证实，EAV 的 ORF5a 蛋白对于病毒感染力很重要，但不是必需的。在这项研究中，我们发现，通过密码子优化的 GP5 在 ORF5 和 ORF5a 之间的重叠区域（1-104 个核苷酸，nt）引入的 RNA 变化对病毒活力具有致命性，这表明 GP5 或 ORF5a 蛋白中的 nt 变化或氨基酸（aa）突变不允许产生感染性病毒。此外，在 1 型（pSHE）和 2 型（pAJXM 和 pAPRRS）全长 PRRSV cDNA 克隆中，ORF5a 表达的失活对于产生感染性病毒是致命的，而通过在转译中表达 ORF5a 蛋白可回收有活力的 PRRSV，这表明 ORF5a 蛋白对于病毒活力是必需的。最后，通过失活下游终止密码子候选物，ORF5a 蛋白可被假定延伸至 63 个氨基酸，从而表明 ORF5a 的 C 末端可能是可变的。
