Klupp B G, Granzow H, Mundt E, Mettenleiter T C
Institute of Molecular Biology, Friedrich-Loeffler-Institutes, Federal Research Centre for Virus Diseases of Animals, D-17498 Insel Riems, Germany.
J Virol. 2001 Oct;75(19):8927-36. doi: 10.1128/JVI.75.19.8927-8936.2001.
Herpesvirus envelopment is a two-step process which includes acquisition of a primary envelope resulting from budding of intranuclear capsids through the inner nuclear membrane. Fusion with the outer leaflet of the nuclear membrane releases nucleocapsids into the cytoplasm, which then gain their final envelope by budding into trans-Golgi vesicles. It has been shown that the UL34 gene product is required for primary envelopment of the alphaherpesvirus pseudorabies virus (PrV) (B. G. Klupp, H. Granzow, and T. C. Mettenleiter, J. Virol. 74:10063-10073, 2000). For secondary envelopment, several virus-encoded PrV proteins are necessary, including glycoproteins E, I, and M (A. R. Brack, J. M. Dijkstra, H. Granzow, B. G. Klupp, and T. C. Mettenleiter, J. Virol. 73:5364-5372, 1999). We show here that the product of the UL37 gene of PrV, which is a constituent of mature virions, is involved in secondary envelopment. Replication of a UL37 deletion mutant, PrV-DeltaUL37, was impaired in normal cells; this defect could be complemented on cells stably expressing UL37. Ultrastructural analysis demonstrated that intranuclear capsid maturation and budding of capsids into and release from the perinuclear space were unimpaired. However, secondary envelopment was drastically reduced. Instead, apparently DNA-filled capsids accumulated in the cytoplasm in large aggregates similar to those observed in the absence of glycoproteins E/I and M but lacking the surrounding electron-dense tegument material. Although displaying an ordered structure, capsids did not contact each other directly. We postulate that the UL37 protein is necessary for correct addition of other tegument proteins, which are required for secondary envelopment. In the absence of the UL37 protein, capsids interact with each other through unknown components but do not acquire the electron-dense tegument which is normally found around wild-type capsids during and after secondary envelopment. Thus, apposition of the UL37 protein to cytoplasmic capsids may be crucial for the addition of other tegument proteins, which in turn are able to interact with viral glycoproteins to mediate secondary envelopment.
疱疹病毒包膜形成是一个两步过程，包括获得由核内衣壳通过内核膜出芽产生的初级包膜。与核膜外小叶融合将核衣壳释放到细胞质中，然后通过出芽进入反式高尔基体囊泡获得最终包膜。已表明UL34基因产物是α疱疹病毒伪狂犬病病毒（PrV）初级包膜形成所必需的（B.G.Klupp、H.Granzow和T.C.Mettenleiter，《病毒学杂志》74:10063 - 10073，2000年）。对于次级包膜形成，几种病毒编码的PrV蛋白是必需的，包括糖蛋白E、I和M（A.R.Brack、J.M.Dijkstra、H.Granzow、B.G.Klupp和T.C.Mettenleiter，《病毒学杂志》73:5364 - 5372，1999年）。我们在此表明，PrV的UL37基因产物作为成熟病毒粒子的一个组成部分，参与次级包膜形成。UL37缺失突变体PrV - DeltaUL37在正常细胞中的复制受损；这种缺陷在稳定表达UL37的细胞上可得到互补。超微结构分析表明，核内衣壳成熟以及衣壳进入和离开核周空间的出芽过程未受损害。然而，次级包膜形成大幅减少。相反，明显充满DNA的衣壳以大聚集体形式积聚在细胞质中，类似于在缺乏糖蛋白E/I和M时观察到的情况，但没有周围电子致密的被膜物质。尽管衣壳呈现有序结构，但它们并不直接相互接触。我们推测，UL37蛋白对于正确添加其他被膜蛋白是必需的，而这些被膜蛋白是次级包膜形成所需要的。在没有UL37蛋白的情况下，衣壳通过未知成分相互作用，但不会获得在次级包膜形成期间和之后通常在野生型衣壳周围发现的电子致密被膜。因此，UL37蛋白与细胞质衣壳的结合对于添加其他被膜蛋白可能至关重要，而这些被膜蛋白反过来能够与病毒糖蛋白相互作用以介导次级包膜形成。
