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。HCMV开放阅读框（ORFs） UL79、-87和95编码的蛋白分别与鼠γ疱疹病毒68 ORFs 18、24和34的晚期基因转录因子同源。为了确定这些HCMV蛋白是否也是β疱疹病毒晚期基因转录所必需的，我们突变了HCMV ORFs UL79，-87和95。重组病毒在高、低感染多重度（MOIs）下感染细胞。在重组病毒中检测到病毒DNA，除非以反式表达野生型病毒蛋白，否则无法检测到感染性病毒。在高MOI下，ORF UL79、-87、或95的突变对主要即刻早期（MIE）基因表达水平或病毒DNA复制没有影响，但未检测到UL44、-75和99 ORF的晚期病毒基因表达。在低MOI条件下，人成纤维细胞中UL79或ul87的预表达（而非UL95）对MIE病毒基因表达水平和病毒DNA复制产生负向影响。ORFs的产物UL79，-87和95作为早期病毒蛋白表达，并在病毒DNA复制开始之前与UL44一起招募到复制前复合物（pre- rc）。这三种HCMV orf对于病毒晚期基因表达和病毒生长都是必不可少的。

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.