Belsham G J
AFRC Institute for Animal Health, Pirbright Laboratory, Woking, Surrey, UK.
EMBO J. 1992 Mar;11(3):1105-10. doi: 10.1002/j.1460-2075.1992.tb05150.x.
The initiation of protein synthesis on foot-and-mouth disease virus RNA occurs at two sites separated by 84 nucleotides. Immediately upstream from the first of these sites is the internal ribosome entry site (IRES), which directs the translation of this RNA to be cap-independent. The utilization of these two initiation sites has been examined using artificial fusion genes in vivo under a variety of conditions. Additional in-frame AUG codons have been introduced between these two authentic start sites to determine the mechanism by which ribosomes recognize the second start site. The results indicate that following internal entry of ribosomes on the 5' side of the first initiation codon, many fail to initiate protein synthesis at this position and scan along the RNA to the second initiation site. In the presence or absence of the IRES both initiation sites are efficiently used but the utilization of the two sites is slightly biased towards the second initiation site by the IRES. Furthermore, in the presence of the IRES, protein synthesis initiates at both sites independently of the activity of the cap-binding complex.
口蹄疫病毒RNA上蛋白质合成的起始发生在两个相隔84个核苷酸的位点。在这些位点中第一个位点的紧邻上游是内部核糖体进入位点（IRES），它指导该RNA的翻译不依赖于帽子结构。在多种条件下，已在体内使用人工融合基因研究了这两个起始位点的利用情况。在这两个真实起始位点之间引入了额外的读框内AUG密码子，以确定核糖体识别第二个起始位点的机制。结果表明，核糖体在第一个起始密码子的5'侧内部进入后，许多核糖体未能在该位置起始蛋白质合成，而是沿着RNA扫描至第二个起始位点。无论有无IRES，两个起始位点均能有效利用，但IRES会使两个位点的利用略微偏向第二个起始位点。此外，在有IRES的情况下，蛋白质合成在两个位点起始，且独立于帽结合复合体的活性。
