Practice question

Box C/D small nucleolar RNAs guide site-specific ribose methylation of ribosomal RNA and small nuclear RNAs. Family defined by conserved sequence motifs Box C UGAUGA and Box D CUGA forming kink-turn structure recognized by Snu13 fifteen-point-five kilodalton protein, NOP56, NOP58, and fibrillarin Nop1 methyltransferase transferring methyl group from S-adenosylmethionine to 2' hydroxyl. Guide duplex upstream of Box D positions target five nucleotides upstream for methylation. Each snoRNA may harbor two guide sequences, D and D' guides, allowing dual modification. Modifications enhance hydrophobic stacking, steric stabilization of helices, and protection from nucleases within catalytic RNA cores.