Li Z, Stahl G, Farabaugh P J
Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore 21250, USA.
RNA. 2001 Feb;7(2):275-84. doi: 10.1017/s135583820100190x.
Like most retroviruses and retrotransposons, the retrotransposon Ty3 expresses its pol gene analog (POL3) as a translational fusion to the upstream gag analog (GAG3). The Gag3-Pol3 fusion occurs by frameshifting during translation of the mRNA that encodes the two separate but overlapping ORFs. We showed previously that the shift occurs by out-of-frame binding of a normal aminoacyl-tRNA in the ribosomal A site caused by an aberrant codonoanticodon interaction in the P site. This event is unlike all previously described programmed translational frameshifts because it does not require tRNA slippage between cognate or near-cognate codons in the mRNA. A sequence of 15 nt distal to the frameshift site stimulates frameshifting 7.5-fold. Here we show that the Ty3 stimulator acts as an unstructured region to stimulate frameshifting. Its function depends on strict spacing from the site of frameshifting. Finally, the stimulator increases frameshifting dependent on sense codon-induced pausing, but has no effect on frameshifting dependent on pauses induced by nonsense codons. Complementarity between the stimulator and a portion of the accuracy center of the ribosome, Helix 18, implies that the stimulator may directly disrupt error correction by the ribosome.
与大多数逆转录病毒和逆转座子一样，逆转座子Ty3将其pol基因类似物（POL3）表达为与上游gag类似物（GAG3）的翻译融合体。Gag3-Pol3融合是在编码两个独立但重叠开放阅读框的mRNA翻译过程中通过移码发生的。我们之前表明，这种移码是由P位点异常的密码子-反密码子相互作用导致核糖体A位点正常氨酰tRNA的框外结合引起的。这一事件不同于所有先前描述的程序性翻译移码，因为它不需要mRNA中同源或近同源密码子之间发生tRNA滑动。移码位点下游15个核苷酸的序列可将移码刺激7.5倍。在这里，我们表明Ty3刺激物作为一个非结构化区域来刺激移码。其功能取决于与移码位点的严格间距。最后，刺激物增加依赖于有义密码子诱导的暂停的移码，但对依赖于无义密码子诱导的暂停的移码没有影响。刺激物与核糖体准确性中心的一部分螺旋18之间的互补性表明，刺激物可能直接破坏核糖体的错误校正。
