Good P J, Welch R C, Barkan A, Somasekhar M B, Mertz J E
McArdle Laboratory for Cancer Research, University of Wisconsin, Madison 53706.
J Virol. 1988 Mar;62(3):944-53. doi: 10.1128/JVI.62.3.944-953.1988.
The late 19S RNAs of simian virus 40 consist of a family of alternatively spliced RNAs, each of which contains open reading frames corresponding to all three of the virion proteins. Two approaches were used to test the hypothesis that each alternatively spliced 19S RNA species is translated to synthesize preferentially only one of the virion proteins. First, we analyzed the synthesis of virion proteins in simian virus 40 mutant-infected monkey cells that accumulate predominantly either only one spliced 19S RNA species or only the 19S RNAs. Second, we determined the virion proteins synthesized in a rabbit reticulocyte lysate programmed with specific, in vitro-transcribed 19S RNA species. These results indicated that VP2 and VP3, but not VP1, are synthesized from all 19S RNA species. Quantitative analysis of these data indicated that individual 19S RNA species containing a translation initiation signal upstream of the VP2 AUG codon were translated in a cell extract three- to fivefold less efficiently than were 19S RNA species lacking this signal and that the precise rate of synthesis of VP2 relative to VP3 varied somewhat with the sequence of the leader region. These data are consistent with the synthesis of VP2 and VP3 occurring by a leaky scanning mechanism in which initiation of translation at a specific AUG codon is affected by both (i) the intrinsic efficiency of ribosomes recognizing the sequences surrounding the AUG codon as an initiation signal and (ii) partial interference from 5'-proximal initiation signals and their corresponding open reading frames.
猴病毒40（Simian virus 40）的晚期19S RNA由一组可变剪接的RNA组成，每个RNA都包含与所有三种病毒粒子蛋白相对应的开放阅读框。我们采用了两种方法来检验以下假设：每个可变剪接的19S RNA种类仅优先翻译合成一种病毒粒子蛋白。首先，我们分析了猴病毒40突变体感染的猴细胞中病毒粒子蛋白的合成情况，这些细胞主要积累仅一种剪接的19S RNA种类或仅积累19S RNA。其次，我们确定了用特定的体外转录19S RNA种类编程的兔网织红细胞裂解物中合成的病毒粒子蛋白。这些结果表明，VP2和VP3可由所有19S RNA种类合成，但VP1并非如此。对这些数据的定量分析表明，在VP2 AUG密码子上游含有翻译起始信号的单个19S RNA种类在细胞提取物中的翻译效率比缺乏该信号的19S RNA种类低三至五倍，并且相对于VP3，VP2的精确合成速率会因前导区序列的不同而有所变化。这些数据与VP2和VP3通过漏扫描机制合成一致，在该机制中，特定AUG密码子处的翻译起始受以下两方面影响：（i）核糖体将AUG密码子周围序列识别为起始信号的内在效率；（ii）5'近端起始信号及其相应开放阅读框的部分干扰。
