Rife J P, Moore P B
Department of Chemistry, Yale University New Haven, CT 06520, USA.
Structure. 1998 Jun 15;6(6):747-56. doi: 10.1016/s0969-2126(98)00076-8.
Ribosomal RNAs contain many modified nucleotides. The functions of these nucleotides are poorly understood and few of them are strongly conserved. The final stem loop in 16S-like rRNAs is an exception in both regards. In both prokaryotes and eukaryotes, the tetranucleotide loop that caps the 3'-terminal stem contains two N6, N6-dimethyladenosine residues. The sequence and pattern of methylation are conserved within the loop, and there is evidence that these methylated nucleotides play an important role in subunit association and the initiation of protein synthesis. Because of the integral role that helix 45 plays in ribosome function, it is important to know what consequences these methylated nucleotides have on its structure.
We have solved the solution structure of a 14-nucleotide analog of the terminal stem loop of bacterial 16S rRNA, which contains N2-methylguanosine as well as two N6,N6-dimethyladenosines.
The methylation of the 16S rRNA stem loop completely alters its conformation, which would otherwise be a GNRA tetraloop. It is likely that the conformation of this loop is crucial for its function, having implications for its interaction with ribosomal subunits and its role in the initiation of protein synthesis.
核糖体RNA含有许多修饰核苷酸。这些核苷酸的功能鲜为人知，且其中很少有高度保守的。16S样rRNA中的最后一个茎环在这两方面都是个例外。在原核生物和真核生物中，位于3'末端茎顶端的四核苷酸环都含有两个N6,N6-二甲基腺苷残基。环内的甲基化序列和模式是保守的，并且有证据表明这些甲基化核苷酸在亚基结合和蛋白质合成起始中起重要作用。由于螺旋45在核糖体功能中起着不可或缺的作用，了解这些甲基化核苷酸对其结构有何影响很重要。
我们解析了细菌16S rRNA末端茎环的一个14核苷酸类似物的溶液结构，该类似物含有N2-甲基鸟苷以及两个N6,N6-二甲基腺苷。
16S rRNA茎环的甲基化完全改变了其构象，否则它将是一个GNRA四环。这个环的构象可能对其功能至关重要，这对它与核糖体亚基的相互作用及其在蛋白质合成起始中的作用具有重要意义。
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