Characterization of varicella-zoster virus-encoded ORFO gene-Comparison of parental and vaccine strains

The varicella-zoster virus (VZV) Oka vaccine strain (vOka) differs from the parental strain (pOka) at several amino acid positions, but the mutations responsible for the attenuation of vOka have not been clearly defined. The ORFO of vOka carries some of the mutations. Although we found that the ORFO of both strains was incorporated into virus particles, the C-terminal region of vOka ORFO was presented on the virion surface and was N-glycosylated, suggesting that the mutation in vOka ORFO changes it into a novel envelope glycoprotein. In a mutant virus in which pOka ORFO was replaced by vOka ORFO, the molecular weight of ORFO was altered, but the plaque size was not. In addition, a pOka recombinant virus lacking the hydrophobic domain of ORFO grew equally well as the wild-type virus, indicating that the mutation in ORFO is not by itself sufficient for the attenuation of the vOka virus. (C) 2010 Elsevier Inc. All rights reserved.