Semmes O J, Chen L, Sarisky R T, Gao Z, Zhong L, Hayward S D
Molecular Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.
J Virol. 1998 Dec;72(12):9526-34. doi: 10.1128/JVI.72.12.9526-9534.1998.
The Epstein-Barr virus (EBV) Zta and Mta regulatory proteins were previously found to be required for efficient replication of oriLyt in cotransfection-replication assays, but the contribution of Mta to the replication process was unknown. We now demonstrate that Mta regulates replication gene expression. Using the polymerase processivity factor BMRF1 as an example, we found that in transfected cells, total BMRF1 mRNA levels were unaffected by Mta but that the amounts of cytoplasmic BMRF1 RNA and protein were greatly increased in the presence of Mta. Mta also increased cytoplasmic accumulation of the BALF2, BALF5, BSLF1, and BBLF4 replication gene mRNAs but did not affect cytoplasmic levels of BBLF2/3 mRNA. Thus, five of the six core replication genes require Mta for efficient accumulation of cytoplasmic RNA. The contribution of Mta to posttranscriptional RNA processing was examined. Examination of Mta localization in transfected cells by indirect immunofluorescence revealed that Mta colocalized with the splicing factor SC35. We also found that Mta has RNA binding activity. Glutathione S-transferase-Mta bound to BMRF1 and BMLF1 transcripts but not to a control cellular gene RNA. Mta contains a consensus leucine-rich nuclear export signal. Such signal sequences are characteristic of proteins that undergo nuclear export. Examination of Mta localization in a heterokaryon assay provided evidence that Mta shuttles between the nucleus and the cytoplasm. Our experiments indicate that Mta functions in RNA processing and transport and mediates cytoplasmic accumulation of a number of EBV early mRNAs.
此前发现在共转染复制试验中，爱泼斯坦 - 巴尔病毒（EBV）的Zta和Mta调节蛋白是oriLyt高效复制所必需的，但Mta在复制过程中的作用尚不清楚。我们现在证明Mta调节复制基因的表达。以聚合酶持续合成因子BMRF1为例，我们发现在转染细胞中，BMRF1的总mRNA水平不受Mta影响，但在有Mta存在的情况下，细胞质中BMRF1 RNA和蛋白质的量大幅增加。Mta还增加了BALF2、BALF5、BSLF1和BBLF4复制基因mRNA的细胞质积累，但不影响BBLF2/3 mRNA的细胞质水平。因此，六个核心复制基因中的五个需要Mta来实现细胞质RNA的有效积累。我们研究了Mta在转录后RNA加工中的作用。通过间接免疫荧光检查转染细胞中Mta的定位，发现Mta与剪接因子SC35共定位。我们还发现Mta具有RNA结合活性。谷胱甘肽S - 转移酶 - Mta与BMRF1和BMLF1转录本结合，但不与对照细胞基因RNA结合。Mta含有一个富含亮氨酸的共有核输出信号。这种信号序列是进行核输出的蛋白质的特征。在异核体试验中检查Mta的定位提供了证据，表明Mta在细胞核和细胞质之间穿梭。我们的实验表明，Mta在RNA加工和运输中起作用，并介导多种EBV早期mRNA的细胞质积累。
