Whetter L E, Day S P, Brown E A, Elroy-Stein O, Lemon S M
Department of Medicine, University of North Carolina, Chapel Hill.
Arch Virol Suppl. 1994;9:291-8. doi: 10.1007/978-3-7091-9326-6_29.
Hepatitis A virus (HAV) exhibits several characteristics which distinguish it from other picornaviruses, including slow growth in cell culture even after adaptation, and lack of host-cell protein synthesis shut-down. Like other picornaviruses, HAV contains a long 5' nontranslated region (NTR) incorporating an internal ribosomal entry site (IRES), which directs cap-independent translation. We compared HAV IRES-initiated translation with translation initiated by the structurally similar encephalomyocarditis virus (EMCV) IRES, using plasmids in which each of the 5'NTRs is linked in-frame with the chloramphenicol acetyltransferase (CAT) gene. Translation was assessed in an HAV-permissive cell line which constitutively expresses T7 RNA polymerase and transcribes high levels of uncapped RNA from these plasmids following transfection. RNAs containing the EMCV IRES were efficiently translated in these cells, while those containing the HAV IRES were translated very poorly. Analysis of translation of these RNAs in the presence of poliovirus protein 2A, which shuts down cap-dependent translation, demonstrated that their translation was cap independent. Our results suggest that the HAV IRES may function poorly in these cells, and that inefficient translation may contribute to the exceptionally slow replication cycle characteristic of cell culture-adapted HAV.
甲型肝炎病毒（HAV）具有一些使其有别于其他小核糖核酸病毒的特征，包括即使经过适应后在细胞培养中生长缓慢，以及不会导致宿主细胞蛋白质合成停止。与其他小核糖核酸病毒一样，HAV含有一个长的5'非翻译区（NTR），其中包含一个内部核糖体进入位点（IRES），该位点指导不依赖帽子结构的翻译。我们使用了一些质粒，其中每个5'NTR都与氯霉素乙酰转移酶（CAT）基因读框相连，比较了HAV IRES起始的翻译与结构相似的脑心肌炎病毒（EMCV）IRES起始的翻译。在一个组成性表达T7 RNA聚合酶的HAV允许性细胞系中评估翻译情况，转染后该细胞系会从这些质粒转录高水平的无帽RNA。含有EMCV IRES的RNA在这些细胞中能有效翻译，而含有HAV IRES的RNA翻译效率很低。在存在脊髓灰质炎病毒蛋白2A（它会抑制依赖帽子结构的翻译）的情况下对这些RNA的翻译进行分析，结果表明它们的翻译不依赖帽子结构。我们的结果表明，HAV IRES在这些细胞中的功能可能较差，翻译效率低下可能导致细胞培养适应型HAV具有异常缓慢的复制周期特征。
