Institute of Biochemistry, National Chung-Hsing University, 145 Xingda Road, Taichung 402, Taiwan.
Int J Mol Sci. 2018 Dec 4;19(12):3867. doi: 10.3390/ijms19123867.
In contrast to -1 programmed ribosomal frameshifting (PRF) stimulation by an RNA pseudoknot downstream of frameshifting sites, a refolding upstream RNA hairpin juxtaposing the frameshifting sites attenuates -1 PRF in human cells and stimulates +1 frameshifting in yeast. This eukaryotic functional mimicry of the internal Shine-Dalgarno (SD) sequence-mediated duplex was confirmed directly in the 70S translation system, indicating that both frameshifting regulation activities of upstream hairpin are conserved between 70S and 80S ribosomes. Unexpectedly, a downstream pseudoknot also possessed two opposing hungry codon-mediated frameshifting regulation activities: attenuation of +1 frameshifting and stimulation of a non-canonical -1 frameshifting within the +1 frameshift-prone CUUUGA frameshifting site in the absence of release factor 2 (RF2) in vitro. However, the -1 frameshifting activity of the downstream pseudoknot is not coupled with its +1 frameshifting attenuation ability. Similarly, the +1 frameshifting activity of the upstream hairpin is not required for its -1 frameshifting attenuation function Thus, each of the mRNA duplexes flanking the two ends of a ribosomal mRNA-binding channel possesses two functions in bi-directional ribosomal frameshifting regulation: frameshifting stimulation and counteracting the frameshifting activity of each other.
与位于框架移位位点下游的 RNA 假结对 -1 核糖体框架移位（PRF）的刺激相反，位于框架移位位点上游的 RNA 发夹的重新折叠会减弱人类细胞中的 -1 PRF，并刺激酵母中的 +1 框架移位。这种真核生物对内部 Shine-Dalgarno（SD）序列介导的双链体的功能模拟在 70S 翻译系统中得到了直接证实，表明上游发夹的两种框架移位调节活性在 70S 和 80S 核糖体之间是保守的。出乎意料的是，下游假结也具有两种相反的饥饿密码子介导的框架移位调节活性：在体外没有释放因子 2（RF2）的情况下，衰减+1 框架移位和刺激+1 框架移位倾向的 CUUUGA 框架移位位点中的非规范 -1 框架移位。然而，下游假结的 -1 框架移位活性与它的 +1 框架移位衰减能力不相关。同样，上游发夹的 +1 框架移位活性不是其 -1 框架移位衰减功能所必需的。因此，核糖体 mRNA 结合通道两端的每个 mRNA 双链体都具有双向核糖体框架移位调节中的两种功能：框架移位刺激和相互抵消框架移位活性。
