Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Nucleic Acids Res. 2012 May;40(9):4071-85. doi: 10.1093/nar/gkr1287. Epub 2011 Dec 30.
Modifications of rRNAs are clustered in functional regions of the ribosome. In Helix 74 of Escherichia coli 23S rRNA, guanosines at positions 2069 and 2445 are modified to 7-methylguanosine(m(7)G) and N(2)-methylguanosine(m(2)G), respectively. We searched for the gene responsible for m(7)G2069 formation, and identified rlmL, which encodes the methyltransferase for m(2)G2445, as responsible for the biogenesis of m(7)G2069. In vitro methylation of rRNA revealed that rlmL encodes a fused methyltransferase responsible for forming both m(7)G2069 and m(2)G2445. We renamed the gene rlmKL. The N-terminal RlmL activity for m(2)G2445 formation was significantly enhanced by the C-terminal RlmK. Moreover, RlmKL had an unwinding activity of Helix 74, facilitating cooperative methylations of m(7)G2069 and m(2)G2445 during biogenesis of 50S subunit. In fact, we observed that RlmKL was involved in the efficient assembly of 50S subunit in a mutant strain lacking an RNA helicase deaD.
rRNA 的修饰集中在核糖体的功能区域。在大肠杆菌 23S rRNA 的螺旋 74 中，位于位置 2069 和 2445 的鸟苷分别被修饰为 7-甲基鸟苷(m(7)G)和 N(2)-甲基鸟苷(m(2)G)。我们搜索了负责 m(7)G2069 形成的基因，并确定了编码 m(2)G2445 甲基转移酶的 rlmL 是负责 m(7)G2069 生物发生的基因。体外 rRNA 甲基化实验表明，rlmL 编码一种融合的甲基转移酶，负责形成 m(7)G2069 和 m(2)G2445。我们将基因重命名为 rlmKL。RlmL 的 N 端活性显著增强了 C 端 RlmK 的 m(2)G2445 形成活性。此外，RlmKL 具有解开螺旋 74 的活性，有利于在 50S 亚基生物发生过程中协同甲基化 m(7)G2069 和 m(2)G2445。事实上，我们观察到 RlmKL 参与了缺乏 RNA 解旋酶 deaD 的突变菌株中 50S 亚基的有效组装。
