Myristoylation of the small envelope protein of porcine reproductive and respiratory syndrome virus is non-essential for virus infectivity but promotes its growth.

The small envelope (E) protein of porcine reproductive and respiratory syndrome virus (PRRSV) is known to possess the properties of an ion-channel protein, and in the present study we show that the PRRSV E protein is N-terminal myristoylated. The PRRSV E protein contains the consensus motif of (1)MGxxxS(6) for myristoylation, and in the presence of 2-hydroxymyristic acid, the virus titer decreased by 2.5 log TCID(50) and the level of viral RNA was reduced significantly. When the glycine at position 2 was mutated to alanine (G2A) using an infectious cDNA clone, a viable virus was recoverable and a mutant PRRSV was obtained. The titers of G2A mutant virus were 2.0 x 10(4) and 1.0 x 10(6)TCID(50)/ml for 'passage-2' and 'passage-3' viruses, respectively, in PAM cells, and these titers were significantly lower than those of wild-type PRRSV. When treated with the myristoylation inhibitor, the G2A mutant virus was resistant to the drug. The data show that the PRRSV E protein myristoylation is non-essential for PRRSV infectivity but promotes the growth of the virus.