Translational Redefinition of UGA Codons Is Regulated by Selenium Availability
Translational Redefinition of UGA Codons Is Regulated by Selenium Availability
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DOI：
10.1074/jbc.m113.481051
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发表时间：
2013-07-05
影响因子：
4.8
通讯作者：
Hatfield, Dolph L.
中科院分区：
文献类型：
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作者：
Howard, Michael T.;Carlson, Bradley A.;Hatfield, Dolph L.
通过翻译重新编码将硒掺入类似于 25 种哺乳动物含硒蛋白中，从而重新定义框内 UGA 密码子以编码含硒氨基酸，硒代半胱氨酸（Sec）。在这里，我们应用核糖体分析来检查膳食硒水平对控制小鼠肝脏中硒蛋白合成的翻译机制的影响。研究表明，膳食硒水平主要通过 UGA 重新定义和 Sec 掺入效率的差异调节在翻译水平上控制基因特异性硒蛋白表达，尽管也观察到对翻译起始和 mRNA 丰度的影响。直接证据表明，增加膳食硒会导致硒蛋白 mRNA 子集的 UGA-Sec 密码子下游核糖体密度大幅增加，并且硒依赖性对 Sec 掺入效率的影响部分是由 Sec-tRNA([Ser]Sec) Um34 甲基化程度介导的。此外，我们发现了硒蛋白子集的 5'-UTR 翻译的证据，以及编码受硒可用性影响最大的硒蛋白的 mRNA 中核糖体停顿在 UGA-Sec 密码子附近的证据。这些数据说明了微量元素硒的膳食水平如何改变遗传密码的读出，从而影响整类蛋白质的表达。
Incorporation of selenium into similar to 25 mammalian selenoproteins occurs by translational recoding whereby in-frame UGA codons are redefined to encode the selenium containing amino acid, selenocysteine (Sec). Here we applied ribosome profiling to examine the effect of dietary selenium levels on the translational mechanisms controlling selenoprotein synthesis in mouse liver. Dietary selenium levels were shown to control gene-specific selenoprotein expression primarily at the translation level by differential regulation of UGA redefinition and Sec incorporation efficiency, although effects on translation initiation and mRNA abundance were also observed. Direct evidence is presented that increasing dietary selenium causes a vast increase in ribosome density downstream of UGA-Sec codons for a subset of selenoprotein mRNAs and that the selenium-dependent effects on Sec incorporation efficiency are mediated in part by the degree of Sec-tRNA([Ser]Sec) Um34 methylation. Furthermore, we find evidence for translation in the 5'-UTRs for a subset of selenoproteins and for ribosome pausing near the UGA-Sec codon in those mRNAs encoding the selenoproteins most affected by selenium availability. These data illustrate how dietary levels of the trace element selenium can alter the readout of the genetic code to affect the expression of an entire class of proteins.