Institute for Cell and Molecular Biology, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.
Nucleic Acids Res. 2017 Feb 28;45(4):2016-2028. doi: 10.1093/nar/gkw842.
Eukaryotic box C/D small nucleolar (sno)RNPs catalyse the site-specific 2΄-O-methylation of ribosomal RNA. The RNA component (snoRNA) contains guide regions that base-pair with the target site to select the single nucleotide to be modified. The terminal C/D and internal C΄/D΄ motifs in the snoRNA, adjacent to the guide region, function as binding sites for the snoRNP proteins including the enzymatic subunit fibrillarin/Nop1. Four yeast snoRNAs are unusual in that they are predicted to methylate two nucleotides in a single target region. In each case, the internal C΄/D΄ motifs from these snoRNAs differ from the consensus. Our data indicate that the C΄/D΄ motifs in snR13, snR48 and U18 form two alternative structures that lead to differences in the position of the proteins bound to this motif. We propose that each snoRNA forms two different snoRNPs, subtly different in how the proteins are bound to the C΄/D΄ motif, leading to 2΄-O-methylation of different nucleotides in the target region. For snR48 and U18, the unusual C΄/D΄ alone is enough for the modification of two nucleotides. However, for the snR13 snoRNA the unusual C΄/D΄ motif and extra base-pairing, which stimulates rRNA 2΄-O-methylation, are both critical for multiple modifications in the target region.
真核生物 box C/D 小核仁 (sno)RNA 核糖核蛋白催化核糖体 RNA 的特异性 2'-O-甲基化。RNA 成分（snoRNA）包含与靶位点配对的引导区域，以选择要修饰的单个核苷酸。snoRNA 中靠近引导区域的末端 C/D 和内部 C' / D' 基序作为 snoRNP 蛋白的结合位点，包括酶亚基 fibrillarin/Nop1。四种酵母 snoRNA 不同寻常的是，它们被预测可以在单个靶区域中甲基化两个核苷酸。在每种情况下，这些 snoRNA 的内部 C' / D' 基序都与共识不同。我们的数据表明，snR13、snR48 和 U18 的 C' / D' 基序形成两种替代结构，导致与该基序结合的蛋白质位置不同。我们提出每个 snoRNA 形成两种不同的 snoRNP，在蛋白质与 C' / D' 基序结合的方式上略有不同，导致靶区域中不同核苷酸的 2'-O-甲基化。对于 snR48 和 U18，仅不寻常的 C' / D' 就足以修饰两个核苷酸。然而，对于 snR13 snoRNA，不寻常的 C' / D' 基序和额外的碱基配对，刺激 rRNA 2'-O-甲基化，对于靶区域中的多个修饰都是至关重要的。
