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. 2015 Apr 28;2015:206849. doi: 10.1155/2015/206849

Figure 1.

Figure 1

(a) Box C/D snoRNAs share two conserved elements: boxes С (PuUGAUGA) and D (CUGA) located at the 5′- and 3′-termini of the RNA molecule, respectively. Often, box C/D snoRNAs also have an additional copy of internally located C′ or D′ boxes. A complex of box C/D snoRNA with nucleolar proteins Nop1p (fibrillarin), Nop56p, Nop58p, and Snu13p (15.5 kDa) catalyzes site-specific 2′-O-methylation of the nucleotide in target RNA. S-Adenosylmethionine (SAM) serves as the donor of the methyl group and is converted to S-adenosylhomocysteine (SAH). (b) Box H/ACA snoRNAs have “hairpin-hinge-hairpin-tail” structure with boxes H (ANANNA) and ACA located within the single-stranded (hinge) and 3′-terminus (tail) regions, respectively. Pseudouridylation complex includes dyskerin (the pseudouridine synthase), GAR1, NHP2, and NOP10 proteins. Box H/ACA snoRNP catalyzes site-specific isomerization of uridine (U) to pseudouridine (Ψ) in target RNA. ∗SnoRNA with target RNA in square brackets designates snoRNP enzyme-substrate complex.