General and Target-Specific RNA Binding Properties of Epstein-Barr Virus SM Posttranscriptional Regulatory Protein
General and Target-Specific RNA Binding Properties of Epstein-Barr Virus SM Posttranscriptional Regulatory Protein
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DOI：
10.1128/jvi.01483-09
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发表时间：
2009-11-15
影响因子：
5.4
通讯作者：
Swaminathan, Sankar
中科院分区：
文献类型：
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作者：
Han, Zhao;Verma, Dinesh;Swaminathan, Sankar
EB病毒（Epstein-Barr virus，EBV）SM蛋白是EBV在复制裂解期早期表达的一种重要的核穿梭蛋白。SM通过结合EBV mRNA并增强大部分EBV裂解周期mRNA的积累来增加EBV裂解基因表达。除了调节RNA剪接之外，SM还增加靶mRNA稳定性和核输出。SM及其在其他疱疹病毒中的同源物已被假设部分通过结合病毒RNA和募集细胞输出因子来发挥功能。虽然SM对基因表达的激活是基因特异性的，但SM是否以特异性方式与mRNA结合或其RNA结合是否是靶非依赖性的尚不清楚。从EBV感染的B淋巴细胞系中分离SM-mRNA复合物，诱导其允许裂解性EBV复制，并通过实时定量逆转录-PCR进行对应于所有已知EBV开放阅读框架的mRNA的定量测量。结果表明，虽然SM具有广泛的RNA结合特性，但在EB病毒mRNA中，SM复合物形成的亲和力存在明显的层次结构。两个最高度SM相关的转录本的体外结合试验表明，SM优先结合某些EBV mRNA的非编码区中存在的特定序列或结构。此外，这些序列的存在赋予了对SM的响应性。这些数据与类似于hnRNP的作用机制一致，hnRNP对基因表达产生序列特异性影响，尽管具有大量RNA共有的多个简并共有结合位点。
Epstein-Barr virus (EBV) SM protein is an essential nuclear shuttling protein expressed by EBV early during the lytic phase of replication. SM acts to increase EBV lytic gene expression by binding EBV mRNAs and enhancing accumulation of the majority of EBV lytic cycle mRNAs. SM increases target mRNA stability and nuclear export, in addition to modulating RNA splicing. SM and its homologs in other herpesvirus have been hypothesized to function in part by binding viral RNAs and recruiting cellular export factors. Although activation of gene expression by SM is gene specific, it is unknown whether SM binds to mRNA in a specific manner or whether its RNA binding is target independent. SM-mRNA complexes were isolated from EBVinfected B-lymphocyte cell lines induced to permit lytic EBV replication, and a quantitative measurement of mRNAs corresponding to all known EBV open reading frames was performed by real-time quantitative reverse transcription-PCR. The results showed that although SM has broad RNA binding properties, there is a clear hierarchy of affinities among EBV mRNAs with respect to SM complex formation. In vitro binding assays with two of the most highly SM-associated transcripts suggested that SM binds preferentially to specific sequences or structures present in noncoding regions of some EBV mRNAs. Furthermore, the presence of these sequences conferred responsiveness to SM. These data are consistent with a mechanism of action similar to that of hnRNPs, which exert sequence-specific effects on gene expression despite having multiple degenerate consensus binding sites common to a large number of RNAs.