The Spatial-Functional Coupling of Box C/D and C′/D′ RNPs Is an Evolutionarily Conserved Feature of the Eukaryotic Box C/D snoRNP Nucleotide Modification Complex

Box C/D ribonucleoprotein particles guide the 2′-O -ribose methylation of target nucleotides in both archaeal and eukaryotic RNAs. These complexes contain two functional centers, assembled around the C/D and C′/D′ motifs in the box C/D RNA. The C/D and C′/D′ RNPs of the archaeal snoRNA-like RNP (sRNP) are spatially and functionally coupled. Here, we show that similar coupling also occurs in eukaryotic box C/D snoRNPs. The C/D RNP guided 2′-O-methylation when the C′/D′ motif was either mutated or ablated. In contrast, the C′/D′ RNP was inactive as an independent complex. Additional experiments demonstrated that the internal C′/D′ RNP is spatially coupled to the terminal box C/D complex. Pulldown experiments also indicated that all four core proteins are independently recruited to the box C/D and C′/D′ motifs. Therefore, the spatial-functional coupling of box C/D and C′/D′ RNPs is an evolutionarily conserved feature of both archaeal and eukaryotic box C/D RNP complexes.