Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
Nucleic Acids Res. 2011 Nov;39(21):9368-75. doi: 10.1093/nar/gkr626. Epub 2011 Aug 8.
Methyltransferases that use S-adenosylmethionine (AdoMet) as a cofactor to catalyse 5-methyl uridine (m(5)U) formation in tRNAs and rRNAs are widespread in Bacteria and Eukaryota, and are also found in certain Archaea. These enzymes belong to the COG2265 cluster, and the Gram-negative bacterium Escherichia coli possesses three paralogues. These comprise the methyltransferases TrmA that targets U54 in tRNAs, RlmC that modifies U747 in 23S rRNA and RlmD that is specific for U1939 in 23S rRNA. The tRNAs and rRNAs of the Gram-positive bacterium Bacillus subtilis have the same three m(5)U modifications. However, as previously shown, the m(5)U54 modification in B. subtilis tRNAs is catalysed in a fundamentally different manner by the folate-dependent enzyme TrmFO, which is unrelated to the E. coli TrmA. Here, we show that methylation of U747 and U1939 in B. subtilis rRNA is catalysed by a single enzyme, YefA that is a COG2265 member. A recombinant version of YefA functions in an E. coli m(5)U-null mutant adding the same two rRNA methylations. The findings suggest that during evolution, COG2265 enzymes have undergone a series of changes in target specificity and that YefA is closer to an archetypical m(5)U methyltransferase. To reflect its dual specificity, YefA is renamed RlmCD.
以 S-腺苷甲硫氨酸（AdoMet）为辅助因子催化 tRNA 和 rRNA 中 5-甲基尿嘧啶（m(5)U）形成的甲基转移酶在细菌和真核生物中广泛存在，也存在于某些古菌中。这些酶属于 COG2265 簇，革兰氏阴性细菌大肠杆菌拥有三个同源物。这些包括靶向 tRNA 中 U54 的甲基转移酶 TrmA、修饰 23S rRNA 中 U747 的 RlmC 和特异性修饰 23S rRNA 中 U1939 的 RlmD。革兰氏阳性细菌枯草芽孢杆菌的 tRNA 和 rRNA 具有相同的三种 m(5)U 修饰。然而，如前所述，枯草芽孢杆菌 tRNA 中的 m(5)U54 修饰是由依赖叶酸的酶 TrmFO 催化的，该酶与大肠杆菌的 TrmA 无关。在这里，我们表明枯草芽孢杆菌 rRNA 中 U747 和 U1939 的甲基化由单个酶 YefA 催化，YefA 是 COG2265 成员。重组形式的 YefA 在大肠杆菌 m(5)U 缺失突变体中发挥作用，添加相同的两个 rRNA 甲基化。这些发现表明，在进化过程中，COG2265 酶在靶标特异性方面发生了一系列变化，并且 YefA 更接近典型的 m(5)U 甲基转移酶。为了反映其双重特异性，YefA 被重新命名为 RlmCD。
