Bousquet-Antonelli C, Henry Y, G'elugne J P, Caizergues-Ferrer M, Kiss T
Laboratoire de Biologie Mol'eculaire Eucaryote du CNRS, Universit'e Paul Sabatier, Toulouse, France.
EMBO J. 1997 Aug 1;16(15):4770-6. doi: 10.1093/emboj/16.15.4770.
Eukaryotic rRNAs possess numerous post-transcriptionally modified nucleotides. The most abundant modifications, 2'-O-ribose methylation and pseudouridylation, occur in the nucleolus during rRNA processing. The nucleolus contains a large number of small nucleolar RNAs (snoRNAs) most of which can be classified into two distinct families defined by conserved sequence boxes and common associated proteins. The C and D box-containing snoRNAs are associated with fibrillarin, and most of them function as guide RNAs in site-specific ribose methylation of rRNAs. The nucleolar function of the other class of snoRNAs, which share box H and ACA elements and are associated with a glycine- and arginine-rich nucleolar protein, Gar1p, remains elusive. Here we demonstrate that the yeast Saccharomyces cerevisiae Gar1 snoRNP protein plays an essential and specific role in the overall pseudouridylation of yeast rRNAs. These results establish a novel function for Gar1 protein and indicate that the box H/ACA snoRNAs, or at least a subset of these snoRNAs, function in the site-specific pseudouridylation of rRNAs.
真核生物的核糖体RNA（rRNA）含有大量转录后修饰的核苷酸。最丰富的修饰，即2'-O-核糖甲基化和假尿苷化，发生在核仁中的rRNA加工过程中。核仁包含大量小核仁RNA（snoRNA），其中大多数可分为两个不同的家族，由保守的序列框和常见的相关蛋白定义。含有C和D框的snoRNA与纤维蛋白原相关，其中大多数在rRNA的位点特异性核糖甲基化中起引导RNA的作用。另一类snoRNA的核仁功能仍然难以捉摸，这类snoRNA共享框H和ACA元件，并与富含甘氨酸和精氨酸的核仁蛋白Gar1p相关。在这里，我们证明酵母酿酒酵母Gar1 snoRNP蛋白在酵母rRNA的整体假尿苷化中起重要且特定的作用。这些结果确立了Gar1蛋白的新功能，并表明框H/ACA snoRNA，或至少这些snoRNA的一个子集，在rRNA的位点特异性假尿苷化中起作用。
