Witherell G W, Schultz-Witherell C S, Wimmer E
RiboGene, Inc., Hayward, California 94545, USA.
Virology. 1995 Dec 20;214(2):660-3. doi: 10.1006/viro.1995.0081.
Translation initiation of encephalomyocarditis virus (EMCV) mRNA occurs by ribosomal entry into the 5' untranslated region. Internal ribosome binding to EMCV mRNA requires a viral cis-acting element, termed the internal ribosomal entry site (IRES), and cellular trans-acting factors. The polypyrimidine tract binding protein (PTB) has been identified as one such trans-acting factor required for EMCV IRES-dependent translation. Using a dicistronic mRNA and an in vitro translation system, we have identified cis-acting elements of the EMCV IRES required for IRES-dependent translation. The results identify several regions of the IRES that are required for efficient IRES-dependent translation, including the PTB binding site. Other regions of the IRES may act only as spacer sequences, analogous to the spacer sequences found in rhinovirus and enterovirus IRES elements, to link essential regions of the IRES together. The flexibility of one region of the EMCV IRES was demonstrated by an insertion of 125 nucleotides that had little effect on IRES function while the constraint imposed on another region was demonstrated by a 3-nucleotide deletion that nearly abolished IRES-dependent translation.
脑心肌炎病毒（EMCV）mRNA的翻译起始是通过核糖体进入5'非翻译区实现的。核糖体与EMCV mRNA的内部结合需要一个病毒顺式作用元件，称为内部核糖体进入位点（IRES），以及细胞反式作用因子。多嘧啶序列结合蛋白（PTB）已被确定为EMCV IRES依赖性翻译所需的一种此类反式作用因子。利用双顺反子mRNA和体外翻译系统，我们确定了IRES依赖性翻译所需的EMCV IRES的顺式作用元件。结果确定了IRES中几个高效IRES依赖性翻译所需的区域，包括PTB结合位点。IRES的其他区域可能仅作为间隔序列，类似于在鼻病毒和肠道病毒IRES元件中发现的间隔序列，将IRES的必需区域连接在一起。EMCV IRES一个区域的灵活性通过插入125个核苷酸得以证明，这对IRES功能影响很小，而另一个区域受到的限制则通过一个3核苷酸缺失得以证明，该缺失几乎消除了IRES依赖性翻译。
