Goto C, Osaka T, Mizutani T
Faculty of Pharmaceutical Sciences, Nagoya City University, Mizuho-ku, Nagoya 467-8603, Japan.
Biofactors. 2001;14(1-4):25-35. doi: 10.1002/biof.5520140105.
For eukaryotic selenoprotein mRNAs, it has been proposed that the SECIS element in the 3'-UTR is required for recognition of UGA as a Sec codon. Some proteins which bind to SECIS (SBP) have been reported. However, it is not clear how the SECIS element in the 3'-UTR can mediate Sec insertion far at the in-frame UGA Sec codons. The idea that there must be a signal near the UGA Sec codon is still being considered. Therefore, we searched for a protein which binds to an RNA sequence surrounding the UGA Sec codon on human GPx mRNA. We found a protein, prepared from bovine brain microsomes, which strongly bound to the RNA fragment upstream of the UGA Sec codon but not to the RNA sequence downstream of the UGA codon. This protein also bound to the SECIS sequence in the 3'-UTR of human GPx, and this binding to SECIS was competed with the RNA fragment upstream of the UGA Sec codon. We also obtained the similar results with the RNA fragments of type I iodothyronine 5'-deiodinase (5'DI) mRNAs. Comparison of such RNA fragments with SECIS fragments revealed similarities in the region upstream of the in-frame UGA Sec codon of several Se-protein mRNAs. The study thus favors a novel model of Sec incorporation at the UGA Sec codon that involves the regions upstream of the UGA codon of mRNAs of mammalian selenoproteins. This model explains that the stem-loop structure covering the UGA codon is recognized by SBP and how the UGA Sec codon escapes from attack by eRF.
对于真核生物硒蛋白mRNA，有人提出3'-UTR中的硒代半胱氨酸插入序列（SECIS）元件是将UGA识别为Sec密码子所必需的。已经报道了一些与SECIS结合的蛋白质（SBP）。然而，尚不清楚3'-UTR中的SECIS元件如何能在框内UGA Sec密码子处介导Sec的插入。UGA Sec密码子附近必须存在信号这一观点仍在被探讨。因此，我们寻找一种能与人谷胱甘肽过氧化物酶（GPx）mRNA上UGA Sec密码子周围的RNA序列结合的蛋白质。我们发现了一种从牛脑微粒体制备的蛋白质，它与UGA Sec密码子上游的RNA片段强烈结合，但不与UGA密码子下游的RNA序列结合。这种蛋白质也与人GPx的3'-UTR中的SECIS序列结合，并且这种与SECIS的结合会被UGA Sec密码子上游的RNA片段竞争。我们用I型碘甲状腺原氨酸5'-脱碘酶（5'DI）mRNA的RNA片段也得到了类似的结果。将这些RNA片段与SECIS片段进行比较，发现几种硒蛋白mRNA的框内UGA Sec密码子上游区域存在相似性。因此，该研究支持一种在UGA Sec密码子处掺入Sec的新模型，该模型涉及哺乳动物硒蛋白mRNA的UGA密码子上游区域。这个模型解释了覆盖UGA密码子的茎环结构如何被SBP识别以及UGA Sec密码子如何避免被真核释放因子（eRF）攻击。
