Transcriptional regulation of herpesviruses dependent on the viral DNA replication

病毒蛋白对人巨细胞病毒(HCMV)晚期基因表达的调控作用尚不清楚。人巨细胞病毒开放阅读框UL79、-87和-95分别编码与小鼠伽马疱疹病毒68ORF 18、24和34晚期基因转录因子同源的蛋白。为了确定这些HCMV蛋白是否对β疱疹病毒的晚期基因转录也是必不可少的，我们突变了HCMV orfUL79、-87和-95。重组病毒分别以高、低感染复数(MOI)感染细胞。当用重组病毒检测到病毒DNA时，除非野生型病毒蛋白以反式方式表达，否则不能检测到传染性病毒。在高MOI时，ORF UL79、-87或-95突变对主要的即刻早期(MIE)基因表达或病毒DNA复制水平没有影响，但未检测到UL44、-75和-99 ORF的晚期病毒基因表达。在低MOI时，UL79或-87在人成纤维细胞中的预表达对MIE病毒基因表达水平和病毒DNA复制水平有负面影响。在病毒DNA复制开始之前，ORF UL79、-87和-95的产物以早期病毒蛋白的形式表达，并与UL44一起被招募到复制前复合体(Pre-RCS)。三个HCMV开放阅读框对于晚期病毒基因表达和病毒生长都是不可或缺的。

The regulation of human cytomegalovirus (HCMV) late gene expression by viral proteins is poorly understood. HCMV open reading frames (ORFs) UL79,-87, and-95 encode proteins with homology to late gene transcription factors of murine gammaherpesvirus 68 ORFs 18, 24, and 34, respectively. To determine whether these HCMV proteins are also essential for late gene transcription of a betaherpesvirus, we mutated HCMV ORFs UL79,-87, and-95. Cells were infected with the recombinant viruses at high and low multiplicities of infection (MOIs). While viral DNA was detected with the recombinant viruses, infectious virus was not detected unless the wild-type viral proteins were expressed in trans. At a high MOI, mutation of ORF UL79,-87, or-95 had no effect on the level of major immediate-early (MIE) gene expression or viral DNA replication, but late viral gene expression from the UL44,-75, and-99 ORFs was not detected. At a low MOI, preexpression of UL79 or-87, but not UL95, in human fibroblast cells negatively affected the level of MIE viral gene expression and viral DNA replication. The products of ORFs UL79,-87, and-95 were expressed as early viral proteins and recruited to prereplication complexes (pre-RCs), along with UL44, before the initiation of viral DNA replication. All three HCMV ORFs are indispensable for late viral gene expression and viral growth.