Center for Molecular Biology and Neuroscience and Institute of Medical Microbiology, Oslo University Hospital, and Department of Molecular Biosciences, University of Oslo, Oslo, Norway.
Mol Cell Biol. 2010 Apr;30(7):1814-27. doi: 10.1128/MCB.01602-09. Epub 2010 Feb 1.
Uridines in the wobble position of tRNA are almost invariably modified. Modifications can increase the efficiency of codon reading, but they also prevent mistranslation by limiting wobbling. In mammals, several tRNAs have 5-methoxycarbonylmethyluridine (mcm5U) or derivatives thereof in the wobble position. Through analysis of tRNA from Alkbh8-/- mice, we show here that ALKBH8 is a tRNA methyltransferase required for the final step in the biogenesis of mcm5U. We also demonstrate that the interaction of ALKBH8 with a small accessory protein, TRM112, is required to form a functional tRNA methyltransferase. Furthermore, prior ALKBH8-mediated methylation is a prerequisite for the thiolation and 2'-O-ribose methylation that form 5-methoxycarbonylmethyl-2-thiouridine (mcm5s2U) and 5-methoxycarbonylmethyl-2'-O-methyluridine (mcm5Um), respectively. Despite the complete loss of all of these uridine modifications, Alkbh8-/- mice appear normal. However, the selenocysteine-specific tRNA (tRNASec) is aberrantly modified in the Alkbh8-/- mice, and for the selenoprotein Gpx1, we indeed observed reduced recoding of the UGA stop codon to selenocysteine.
tRNA 摆动位置的尿嘧啶几乎总是被修饰的。修饰可以提高密码子阅读的效率，但也可以通过限制摆动来防止错译。在哺乳动物中，几种 tRNA 在摆动位置具有 5-甲酰基甲硫基尿嘧啶(mcm5U)或其衍生物。通过对 Alkbh8-/-小鼠的 tRNA 分析，我们在这里表明，ALKBH8 是一种 tRNA 甲基转移酶，是 mcm5U 生物发生的最后一步所必需的。我们还证明，ALKBH8 与一个小辅助蛋白 TRM112 的相互作用对于形成功能性 tRNA 甲基转移酶是必需的。此外，ALKBH8 介导的甲基化是硫代和 2'-O-核糖甲基化形成 5-甲酰基甲硫基-2-硫尿嘧啶(mcm5s2U)和 5-甲酰基甲硫基-2'-O-甲基尿嘧啶(mcm5Um)的前提。尽管所有这些尿嘧啶修饰完全缺失，但 Alkbh8-/-小鼠似乎正常。然而，Alkbh8-/-小鼠中的硒代半胱氨酸特异性 tRNA(tRNASec)被异常修饰，对于硒蛋白 Gpx1，我们确实观察到 UGA 终止密码子到硒代半胱氨酸的重新编码减少。
