The capsid-associated UL25 protein of the alphaherpesvirus pseudorabies virus is nonessential for cleavage and encapsidation of genomic DNA but is required for nuclear egress of capsids
The capsid-associated UL25 protein of the alphaherpesvirus pseudorabies virus is nonessential for cleavage and encapsidation of genomic DNA but is required for nuclear egress of capsids
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DOI：
10.1128/jvi.02662-05
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发表时间：
2006-07-01
影响因子：
5.4
通讯作者：
Mettenleiter, Thomas C.
中科院分区：
文献类型：
--
作者：
Klupp, Barbara G.;Granzow, Harald;Mettenleiter, Thomas C.
单纯疱疹病毒UL25基因产物在疱疹病毒科的三个亚家族中都已被鉴定为同源基因。然而，它们在病毒复制过程中的确切功能尚不清楚。鉴于早期的研究表明，HSV-1的UL25蛋白不是切割新复制的病毒DNA所必需的，而是稳定包裹所必需的(A.R.McNab，P.Desai，S.Person，L.Roof，D.R.Thompson，W.W.Newcomb，J.C.Brown，和F.L.Homa，J.Virol。72：1060-1070,1998)，病毒DNA包装最近被证明在没有UL25的情况下发生，尽管与野生型HSV-1相比水平显著降低(N.Stow，J.Virol)。75：10755-10765 2001年)。为了阐明UL25的功能，我们分析了甲型疱疹病毒伪狂犬病病毒(PRV)的同源蛋白。PRV UL25被发现对病毒复制是必不可少的，因为缺乏UL25蛋白的突变病毒需要表达UL25的细胞才能进行生产性繁殖。在没有UL25蛋白的情况下，新复制的PRV DNA被切割，并在感染的细胞核中检测到含有DNA的C型衣壳。然而，尽管衣壳经常与内核膜密切相关，但没有观察到核外流。因此，在细胞质中没有发现衣壳，从而抑制了病毒粒子的形态发生。相反，在细胞质中很容易观察到无衣壳被膜结构(L颗粒)的形成。因此，我们的数据表明，PRV UL25蛋白对病毒基因组的切割和封装不是必不可少的，尽管这两个过程在蛋白质存在的情况下都更有效。然而，PRV UL25蛋白的存在是核出口的先决条件。通过免疫电子显微镜，我们在含DNA的C衣壳上检测到UL25特异性标记，而在其他核内未成熟或有缺陷的衣壳形式上未检测到UL25特异性标记。因此，PRV UL25蛋白可能代表了迄今为止缺失的触发器，该触发器最好允许DNA填充的C衣壳的初级包膜。
Homologs of the UL25 gene product of herpes simplex virus (HSV) have been identified in all three subfamilies of the Herpesviridae. However, their exact function during viral replication is not yet known. Whereas earlier studies indicated that the UL25 protein of HSV-1 is not required for cleavage of newly replicated viral DNA but is necessary for stable encapsidation (A.R.McNab, P.Desai, S.Person, L.Roof, D.R.Thompson, W.W.Newcomb, J.C.Brown, and F.L.Homa, J.Virol. 72:1060-1070,1998), viral DNA packaging has recently been demonstrated to occur in the absence of UL25, although at significantly decreased levels compared to wild-type HSV-1 (N. Stow, J. Virol. 75:10755-10765 2001). To clarify the functional role of UL25 we analyzed the homologous protein of the alphaherpesvirus pseudorabies virus (PrV). PrV UL25 was found to be essential for viral replication, as a mutant virus lacking the UL25 protein required UL25-expressing cells for productive propagation. In the absence of the UL25 protein, newly replicated PrV DNA was cleaved and DNA-containing C-type capsids were detected in infected cell nuclei. However, although capsids were frequently found in close association with the inner nuclear membrane, nuclear egress was not observed. Consequently, no capsids were found in the cytoplasm, resulting in an inhibition of virion morphogenesis. In contrast, the formation of capsidless enveloped tegument structures (L particles) in the cytoplasm was readily observed. Thus, our data demonstrate that the PrV UL25 protein is not essential for cleavage and encapsidation of viral genomes, although both processes occur more efficiently in the presence of the protein. However, the presence of the PrV UL25 protein is a prerequisite for nuclear egress. By immunoelectron microscopy, we detected UL25-specific label on DNA-containing C capsids but not on other intranuclear immature or defective capsid forms. Thus, the PrV UL25 protein may represent the hitherto missing trigger that allows primary envelopment preferably of DNA-filled C capsids.