Laboratory of Virology and Vaccinology, Division of Biomedical Research, National Institute of Biomedical Innovation, 7-6-8, Saito-Asagi, Ibaraki, Osaka 567-0085, Japan.
J Virol. 2010 Apr;84(7):3488-502. doi: 10.1128/JVI.01838-09. Epub 2010 Jan 27.
The ORF50 gene of the varicella-zoster virus (VZV) encodes glycoprotein M (gM), which is conserved among all herpesviruses and is important for the cell-to-cell spread of VZV. However, few analyses of ORF50 gene expression or its posttranscriptional and translational modifications have been published. Here we found that in VZV-infected cells, ORF50 encoded four transcripts: a full-size transcript, which was translated into the gM, and three alternatively spliced transcripts, which were not translated. Using a splicing-negative mutant virus, we showed that the alternative transcripts were nonessential for viral growth in cell culture. In addition, we found that two amino acid mutations of gM, V42P and G301M, blocked gM's maturation and transport to the trans-Golgi network, which is generally recognized as the viral assembly complex. We also found that the mutations disrupted gM's interaction with glycoprotein N (gN), revealing their interaction through a bond that is otherwise unreported for herpesviruses. Using this gM maturation-negative virus, we found that immature gM and gN were incorporated into intracellularly isolated virus particles and that mature gM was required for efficient viral growth via cell-to-cell spread but not for virion morphogenesis. The virus particles were more abundant at the abnormally enlarged perinuclear cisternae than those of the parental virus, but they were also found at the cell surface and in the culture medium. Additionally, in the gM maturation-negative mutant virus-infected melanoma cells, typical syncytium formation was rarely seen, again indicating that mature gM functions in cell-to-cell spread via enhancement of syncytium formation.
水痘带状疱疹病毒（VZV）的 ORF50 基因编码糖蛋白 M（gM），该蛋白在所有疱疹病毒中都保守，对 VZV 的细胞间传播很重要。然而，ORF50 基因表达或其转录后和翻译后修饰的分析很少有报道。在这里，我们发现 VZV 感染的细胞中，ORF50 编码四种转录本：一种全长转录本，翻译成 gM，和三种选择性剪接转录本，不进行翻译。使用剪接阴性突变病毒，我们表明，替代转录本对于病毒在细胞培养中的生长不是必需的。此外，我们发现 gM 的两个氨基酸突变 V42P 和 G301M 阻断了 gM 的成熟和向反式高尔基体网络的运输，反式高尔基体网络通常被认为是病毒组装复合物。我们还发现，这些突变破坏了 gM 与糖蛋白 N（gN）的相互作用，揭示了它们之间的相互作用，这种相互作用在疱疹病毒中是没有报道过的。使用这种 gM 成熟阴性病毒，我们发现不成熟的 gM 和 gN 被纳入细胞内分离的病毒粒子中，成熟的 gM 对于通过细胞间传播有效生长是必需的，但对于病毒形态发生不是必需的。与亲本病毒相比，病毒粒子在异常增大的核周池内更丰富，但也在细胞表面和培养基中发现。此外，在 gM 成熟阴性突变病毒感染的黑色素瘤细胞中，很少看到典型的合胞体形成，这再次表明成熟的 gM 通过增强合胞体形成在细胞间传播中发挥作用。
