Jang S K, Wimmer E
Department of Microbiology, State University of New York, Stony Brook 11794.
Genes Dev. 1990 Sep;4(9):1560-72. doi: 10.1101/gad.4.9.1560.
Translation of encephalomyocarditis virus (EMCV) mRNA occurs by ribosomal internal entry into the 5'-nontranslated region (5' NTR) rather than by ribosomal scanning. The internal ribosomal entry site (IRES) in the EMCV 5' NTR was determined by in vitro translation with RNAs that were generated by in vitro transcription of EMCV cDNAs containing serial deletions from either the 5' or 3' end of the EMCV 5' NTR. Regions downstream of nucleotide 403 and upstream of nucleotide 811 of EMCV were required for efficient translation. Site-directed mutagenesis revealed that a stem-loop structure (400 nucleotides upstream of the initiation codon) was essential for IRES function. We discovered a 57-kD cellular protein whose specific interaction with this stem-loop appears to be prerequisite for IRES function. A A pyrimidine-rich stretch proximal to the initiation codon was also crucial for efficient translation of EMCV mRNA. We propose that ribosomes bind directly to the initiating AUG without scanning.
脑心肌炎病毒（EMCV）信使核糖核酸（mRNA）的翻译是通过核糖体内部进入5'-非翻译区（5'NTR）实现的，而非核糖体扫描。EMCV 5'NTR中的内部核糖体进入位点（IRES）是通过用RNA进行体外翻译来确定的，这些RNA是由对包含从EMCV 5'NTR 5'或3'末端连续缺失的EMCV互补DNA（cDNA）进行体外转录产生的。EMCV核苷酸403下游和核苷酸811上游的区域是有效翻译所必需的。定点诱变表明，一个茎环结构（起始密码子上游400个核苷酸）对IRES功能至关重要。我们发现了一种57-kD的细胞蛋白，其与该茎环的特异性相互作用似乎是IRES功能的先决条件。起始密码子近端富含嘧啶的片段对EMCV mRNA的有效翻译也至关重要。我们提出核糖体直接结合到起始甲硫氨酸密码子（AUG）上而不进行扫描。
