Long M C, Leong V, Schaffer P A, Spencer C A, Rice S A
Departments of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
J Virol. 1999 Jul;73(7):5593-604. doi: 10.1128/JVI.73.7.5593-5604.1999.
Herpes simplex virus type 1 (HSV-1) infection alters the phosphorylation of the large subunit of RNA polymerase II (RNAP II), resulting in the depletion of the hypophosphorylated and hyperphosphorylated forms of this polypeptide (known as IIa and IIo, respectively) and induction of a novel, alternatively phosphorylated form (designated IIi). We previously showed that the HSV-1 immediate-early protein ICP22 is involved in this phenomenon, since induction of IIi and depletion of IIa are deficient in cells infected with 22/n199, an HSV-1 ICP22 nonsense mutant (S. A. Rice, M. C. Long, V. Lam, P. A. Schaffer, and C. A. Spencer, J. Virol. 69:5550-5559, 1995). However, depletion of IIo still occurs in 22/n199-infected cells. This suggests either that another viral gene product affects the RNAP II large subunit or that the truncated ICP22 polypeptide encoded by 22/n199 retains residual activity which leads to IIo depletion. To distinguish between these possibilities, we engineered an HSV-1 ICP22 null mutant, d22-lacZ, and compared it to 22/n199. The two mutants are indistinguishable in their effects on the RNAP II large subunit, suggesting that an additional viral gene product is involved in altering RNAP II. Two candidates are UL13, a protein kinase which has been implicated in ICP22 phosphorylation, and the virion host shutoff (Vhs) factor, the expression of which is positively regulated by ICP22 and UL13. To test whether UL13 is involved, a UL13-deficient viral mutant, d13-lacZ, was engineered. This mutant was defective in IIi induction and IIa depletion, displaying a phenotype very similar to that of d22-lacZ. In contrast, a Vhs mutant had effects that were indistinguishable from wild-type HSV-1. Therefore, UL13 but not the Vhs function plays a role in modifying the RNAP II large subunit. To study the potential role of UL13 in viral transcription, we carried out nuclear run-on transcription analyses in infected human embryonic lung cells. Infections with either UL13 or ICP22 mutants led to significantly reduced amounts of viral genome transcription at late times after infection. Together, our results suggest that ICP22 and UL13 are involved in a common pathway that alters RNAP II phosphorylation and that in some cell lines this change promotes viral late transcription.
1型单纯疱疹病毒（HSV-1）感染会改变RNA聚合酶II（RNAP II）大亚基的磷酸化状态，导致该多肽的低磷酸化和高磷酸化形式（分别称为IIa和IIo）减少，并诱导产生一种新的、经过不同磷酸化修饰的形式（命名为IIi）。我们之前发现，HSV-1的立即早期蛋白ICP22参与了这一现象，因为在感染了HSV-1 ICP22无义突变体22/n199的细胞中，IIi的诱导和IIa的减少存在缺陷（S. A. Rice、M. C. Long、V. Lam、P. A. Schaffer和C. A. Spencer，《病毒学杂志》69:5550 - 5559，1995年）。然而，在感染22/n199的细胞中，IIo的减少仍然会发生。这表明要么是另一种病毒基因产物影响了RNAP II大亚基，要么是由22/n199编码的截短的ICP22多肽保留了导致IIo减少的残余活性。为了区分这两种可能性，我们构建了一个HSV-1 ICP22缺失突变体d22-lacZ，并将其与22/n199进行比较。这两种突变体对RNAP II大亚基的影响没有区别，表明还有一种额外的病毒基因产物参与了RNAP II的改变。有两个候选基因，一个是UL13，一种与ICP22磷酸化有关的蛋白激酶，另一个是病毒体宿主关闭（Vhs）因子，其表达受ICP22和UL13的正向调控。为了测试UL13是否参与其中，构建了一个UL13缺陷型病毒突变体d13-lacZ。该突变体在IIi诱导和IIa减少方面存在缺陷，表现出与d22-lacZ非常相似的表型。相比之下，一个Vhs突变体的影响与野生型HSV-1没有区别。因此，是UL13而不是Vhs功能在修饰RNAP II大亚基中发挥作用。为了研究UL13在病毒转录中的潜在作用，我们在感染的人胚肺细胞中进行了细胞核连续转录分析。用UL13或ICP22突变体感染后，在感染后期病毒基因组转录量显著减少。总之，我们的结果表明，ICP22和UL13参与了一条共同的途径，该途径改变了RNAP II的磷酸化状态，并且在某些细胞系中这种变化促进了病毒晚期转录。
