Yamashita Yui, Lambein Ingrid, Kobayashi Soko, Onouchi Hitoshi, Chiba Yukako, Naito Satoshi
Graduate School of Life Science, Hokkaido University.
Genes Genet Syst. 2013;88(4):241-9. doi: 10.1266/ggs.88.241.
Cystathionine γ-synthase (CGS) catalyzes the first committed step of methionine (Met) biosynthesis in plants. Expression of the Arabidopsis thaliana CGS1 gene is negatively feedback-regulated in response to the direct Met metabolite S-adenosyl-L-methionine (AdoMet). This regulation occurs at the step of mRNA stability during translation and is coupled with AdoMet-induced CGS1-specific translation arrest. In general, mRNA decay is initiated by a shortening of the poly(A) tail. However, this process has not been studied in detail in cases where regulatory events, such as programmed translation arrest, are involved. Here, we report that the poly(A) tail of the full-length CGS1 mRNA showed an apparent increase from 50-80 nucleotides (nt) to 140-150 nt after the induction of CGS1 mRNA degradation. This finding was unexpected because mRNAs that are destined for degradation harbored longer poly(A) tail than mRNAs that were not targeted for degradation. The results suggest that poly(A) shortening is inhibited or delayed during AdoMet-induced translation arrest of CGS1 mRNA. We propose an explanation for this phenomenon that remains consistent with the recent model of actively translating mRNA. We also found that CGS1 mRNA degradation intermediates, which are 5'-truncated forms of CGS1 mRNA, had a short poly(A) tail of 10-30 nt. This suggests that poly(A) shortening occurs rapidly on the degradation intermediates. The present study highlights CGS1 mRNA degradation as a useful system to understand the dynamic features of poly(A) shortening.
胱硫醚γ-合酶（CGS）催化植物中蛋氨酸（Met）生物合成的首个关键步骤。拟南芥CGS1基因的表达会因直接的Met代谢产物S-腺苷-L-蛋氨酸（AdoMet）而受到负反馈调节。这种调节发生在翻译过程中mRNA稳定性这一步骤，并且与AdoMet诱导的CGS1特异性翻译停滞相关联。一般来说，mRNA降解是由多聚腺苷酸（poly(A)）尾巴缩短引发的。然而，在涉及诸如程序性翻译停滞等调控事件的情况下，这一过程尚未得到详细研究。在此，我们报告称，在诱导CGS1 mRNA降解后，全长CGS1 mRNA的poly(A)尾巴明显从50 - 80个核苷酸（nt）增加到140 - 150 nt。这一发现出人意料，因为注定要降解的mRNA比未被靶向降解的mRNA含有更长的poly(A)尾巴。结果表明，在AdoMet诱导CGS1 mRNA翻译停滞期间，poly(A)缩短受到抑制或延迟。我们针对这一现象提出了一种解释，该解释与近期关于活跃翻译mRNA的模型相一致。我们还发现，CGS1 mRNA降解中间体，即CGS1 mRNA的5'端截短形式，具有10 - 30 nt的短poly(A)尾巴。这表明poly(A)缩短在降解中间体上迅速发生。本研究突出了CGS1 mRNA降解作为理解poly(A)缩短动态特征的一个有用系统。
