生化细胞所发现人胞质ArgRS的mRNA能够独立招募大肠杆菌核糖体

摘要 : 中国科学院上海生物化学与细胞生物学研究所王恩多研究组发现，大肠杆菌也能够产生跟人胞质中一样的长短两种不同形式的精氨酰-tRNA合成酶(ArgRS)，并进一步发现，全长hcArgRS的N-末端延伸区的mRNA在大肠杆菌细胞中能够独立招募核糖体，并通过内部起始的机制产生短形式hcArgRS。相关文章发表于2014年6月4日的《Journal of Biological Chemistry》杂志上。

在人胞质中，九种氨基酰-tRNA合成酶(aaRS)和三种辅助蛋白因子构成了一个巨大的氨基酰-tRNA合成酶复合物(MSC)。另外，人细胞中存在长短两种不同形式的精氨酰-tRNA合成酶(ArgRS)，全长形式的ArgRS参与MSC的组装，短形式的ArgRS在N-末端缺少72个氨基酸，在人胞质中以游离形式存在。这两种不同形式的ArgRS是由同一条mRNA在不同的起始位点翻译产生的。

王恩多研究组的杨芳博士等人发现当在大肠杆菌细胞中过表达人细胞质ArgRS(hcArgRS)的基因时，也会产生长短两种不同的形式，而且与在人胞质中的两种形式完全相同。进一步的研究发现，全长hcArgRS的N-末端延伸区的mRNA在大肠杆菌细胞中能够独立招募核糖体，并通过内部起始的机制产生短形式hcArgRS。该研究对于阐明hcArgRS的mRNA翻译重起始的发生机理起到一定的提示作用。

该研究还得到国家自然科学基金和国家基础研究基金的资助。

原文摘要：

The mRNA of Human Cytoplasmic Arginyl-tRNA Synthetase Recruits Prokaryotic Ribosome Independently

Fang Yang, Quan-Quan Ji, Liang-Liang Ruan, Qing Ye andEn-Duo Wang

There are two isoforms of cytoplasmic arginyl-tRNA synthetase(hcArgRS) in human cells. The long form is a component of the multiple aminoacyl-tRNA synthetase complex and the other is a N-terminal truncated form (ΔNhcArgRS), free in the cytoplasm. It has been shown that the two forms of ArgRS arise from alternative translational initiation in a single mRNA. The short form is produced from the initiation at a downstream in-frame AUG start codon. Interestingly, our data suggest that the alternative translational initiation of hcArgRS mRNA also takes place in E. coli transformants . When the gene encoding full-length hcArgRS was over-expressed in E. coli, two forms of hcArgRS were observed. The N-terminal sequencing experiment identified that the short form was identical to the ΔNhcArgRS in human cytoplasm. By constructing a bicistronic system, our data support that the mRNA encoding N-terminal extension of hcArgRS has the capacity of independently recruiting E. coli ribosome. Furthermore, two critical elements for recruiting the prokaryotic ribosome were identified, the "AGGA" core of Shine-Dalgarno sequence and the "A-rich" sequence located just proximal to the alternative in-frame initiation site. Although the mechanisms of prokaryotic and eukaryotic translational initiation are distinct, they share some common features. The ability of the hcArgRS mRNA to recruit the prokaryotic ribosome may provide clues for shedding light on the mechanism of alternative translational initiation of hcArgRS mRNA in eukaryotic cells.

作者：生化细胞所

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