Department of Molecular Biology, The Jikei University School of Medicine, 3-25-8 Nishi-shimbashi, Minato-Ku, Tokyo 105-8461, Japan.
Department of Applied Chemistry, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji 671-2280, Japan.
J Biochem. 2020 Aug 1;168(2):139-149. doi: 10.1093/jb/mvaa032.
Antizyme (AZ) interacts with ornithine decarboxylase, which catalyzes the first step of polyamine biosynthesis and recruits it to the proteasome for degradation. Synthesizing the functional AZ protein requires transition of the reading frame at the termination codon. This programmed +1 ribosomal frameshifting is induced by polyamines, but the molecular mechanism is still unknown. In this study, we explored the mechanism of polyamine-dependent +1 frameshifting using a human cell-free translation system. Unexpectedly, spermidine induced +1 frameshifting in the mutants replacing the termination codon at the shift site with a sense codon. Truncation experiments showed that +1 frameshifting occurred promiscuously in various positions of the AZ sequence. The probability of this sequence-independent +1 frameshifting increased in proportion to the length of the open reading frame. Furthermore, the +1 frameshifting was induced in some sequences other than the AZ gene in a polyamine-dependent manner. These findings suggest that polyamines have the potential to shift the reading frame in the +1 direction in any sequence. Finally, we showed that the probability of the sequence-independent +1 frameshifting by polyamines is likely inversely correlated with translation efficiency. Based on these results, we propose a model of the molecular mechanism for AZ +1 frameshifting.
抗酶（AZ）与鸟氨酸脱羧酶相互作用，后者催化多胺生物合成的第一步，并将其招募到蛋白酶体进行降解。合成功能性 AZ 蛋白需要终止密码子处的阅读框转换。这种程序性+1 核糖体移码是由多胺诱导的，但分子机制尚不清楚。在这项研究中，我们使用人无细胞翻译系统探索了多胺依赖性+1 移码的机制。出乎意料的是，亚精胺诱导移码位点终止密码子被同义密码子取代的突变体发生+1 移码。截断实验表明，+1 移码在 AZ 序列的各种位置随机发生。这种序列非依赖性+1 移码的概率与开放阅读框的长度成正比增加。此外，多胺以依赖多胺的方式在 AZ 基因以外的某些序列中诱导+1 移码。这些发现表明，多胺有可能在任何序列中以+1 方向移动阅读框。最后，我们表明多胺诱导的序列非依赖性+1 移码的概率可能与翻译效率成反比。基于这些结果，我们提出了 AZ+1 移码的分子机制模型。
