Human Cytomegalovirus Early Protein pUL21a Promotes Efficient Viral DNA Synthesis and the Late Accumulation of Immediate-Early Transcripts
Human Cytomegalovirus Early Protein pUL21a Promotes Efficient Viral DNA Synthesis and the Late Accumulation of Immediate-Early Transcripts
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DOI：
10.1128/jvi.01599-10
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发表时间：
2011-01-01
影响因子：
5.4
通讯作者：
Yu, Dong
中科院分区：
文献类型：
--
作者：
Fehr, Anthony R.;Yu, Dong
我们以前曾报道，一个新注释的人巨细胞病毒（HCMV）基因，UL 21 a，编码一个早期病毒蛋白命名为pUL 21 a。最值得注意的是，UL 21 a缺失病毒的病毒粒子具有显著降低的感染性，表明需要UL 21 a来建立有效的生产性感染。在这项研究中，我们用等量的含DNA的病毒颗粒感染成纤维细胞，并确定了病毒生命周期中pUL 21 a的作用部位。UL 21 a缺失病毒进入细胞并有效地启动病毒基因表达;然而，它合成病毒DNA很差，并在感染后期以降低的水平积累了几种立即早期（IE）转录本。病毒DNA合成的缺陷先于基因表达的缺陷，并且抑制病毒DNA合成将野生型和突变病毒感染的细胞中IE转录物的后期积累降低到相等的水平。这表明病毒DNA合成减少是在不存在UL 21 a的情况下IE基因表达减少的原因。UL 21 a缺失病毒的生长类似于重组HCMV，其中pUL 21 a表达被终止密码子突变废除，并且缺陷在pUL 21 a表达的成纤维细胞中被挽救。pUL 21 a的反式表达足以恢复正常成纤维细胞产生的突变病毒的病毒DNA合成和基因表达，而由互补细胞产生的突变病毒在正常成纤维细胞中仍表现出缺陷。因此，pUL 21 a不促进HCMV病毒粒子的功能;相反，其从头合成促进病毒DNA合成，这对于IE转录物的后期积累和建立生产性感染是必需的。
We have previously reported that a newly annotated gene of human cytomegalovirus (HCMV), UL21a, encodes an early viral protein termed pUL21a. Most notably, the virions of a UL21a deletion virus had markedly reduced infectivity, indicating that UL21a is required to establish an efficient productive infection. In this study, we infected fibroblasts with equal numbers of DNA-containing viral particles and identified where in the viral life cycle pUL21a acted. The UL21a deletion virus entered cells and initiated viral gene expression efficiently; however, it synthesized viral DNA poorly and accumulated several immediate-early (IE) transcripts at reduced levels at late times of infection. The defect in viral DNA synthesis preceded that in gene expression, and inhibition of viral DNA synthesis reduced the late accumulation of IE transcripts in both wild-type and mutant virus-infected cells to equivalent levels. This suggests that reduced viral DNA synthesis is the cause of reduced IE gene expression in the absence of UL21a. The growth of UL21a deletion virus was similar to that of recombinant HCMV in which pUL21a expression was abrogated by stop codon mutations, and the defect was rescued in pUL21a-expressing fibroblasts. pUL21a expression in trans was sufficient to restore viral DNA synthesis and gene expression of mutant virus produced from normal fibroblasts, whereas mutant virus produced from complementing cells still exhibited the defect in normal fibroblasts. Thus, pUL21a does not promote the functionality of HCMV virions; rather, its de novo synthesis facilitates viral DNA synthesis, which is necessary for the late accumulation of IE transcripts and establishment of a productive infection.