Mariotti Marco, Shetty Sumangala, Baird Lisa, Wu Sen, Loughran Gary, Copeland Paul R, Atkins John F, Howard Michael T
Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA USA.
Department of Biochemistry and Molecular Biology, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ USA.
Nucleic Acids Res. 2017 Dec 15;45(22):13004-13015. doi: 10.1093/nar/gkx982.
Gene-specific expansion of the genetic code allows for UGA codons to specify the amino acid selenocysteine (Sec). A striking example of UGA redefinition occurs during translation of the mRNA coding for the selenium transport protein, selenoprotein P (SELENOP), which in vertebrates may contain up to 22 in-frame UGA codons. Sec incorporation at the first and downstream UGA codons occurs with variable efficiencies to control synthesis of full-length and truncated SELENOP isoforms. To address how the Selenop mRNA can direct dynamic codon redefinition in different regions of the same mRNA, we undertook a comprehensive search for phylogenetically conserved RNA structures and examined the function of these structures using cell-based assays, in vitro translation systems, and in vivo ribosome profiling of liver tissue from mice carrying genomic deletions of 3' UTR selenocysteine-insertion-sequences (SECIS1 and SECIS2). The data support a novel RNA structure near the start codon that impacts translation initiation, structures located adjacent to UGA codons, additional coding sequence regions necessary for efficient production of full-length SELENOP, and distinct roles for SECIS1 and SECIS2 at UGA codons. Our results uncover a remarkable diversity of RNA elements conducting multiple occurrences of UGA redefinition to control the synthesis of full-length and truncated SELENOP isoforms.
遗传密码的基因特异性扩展使得UGA密码子能够编码氨基酸硒代半胱氨酸（Sec）。UGA重新定义的一个显著例子发生在编码硒转运蛋白硒蛋白P（SELENOP）的mRNA翻译过程中，在脊椎动物中，该蛋白可能含有多达22个符合读框的UGA密码子。在第一个和下游UGA密码子处掺入Sec的效率各不相同，以控制全长和截短的SELENOP异构体的合成。为了研究Selenop mRNA如何在同一mRNA的不同区域指导动态密码子重新定义，我们全面搜索了系统发育保守的RNA结构，并使用基于细胞的检测、体外翻译系统以及对携带3'UTR硒代半胱氨酸插入序列（SECIS1和SECIS2）基因组缺失的小鼠肝脏组织进行体内核糖体分析，来研究这些结构的功能。数据支持起始密码子附近存在一种影响翻译起始的新型RNA结构、与UGA密码子相邻的结构、有效产生全长SELENOP所需的额外编码序列区域，以及SECIS1和SECIS2在UGA密码子处的不同作用。我们的结果揭示了多种RNA元件的显著多样性，这些元件多次进行UGA重新定义以控制全长和截短的SELENOP异构体的合成。
