Box C/D snoRNP catalysed methylation is aided by additional pre-rRNA base-pairing

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• 2 -O-methylation of eukaryotic ribosomal RNA (rRNA) is crucial for ribosome function and is catalyzed by box C/D small nucleolar ribonucleoprotein complexes (snoRNPs).
• The RNA components (snoRNAs) of snoRNPs guide the modification to specific rRNA sites via base-pairing with guide sequences.

Purpose of the Study:

• To investigate novel conserved sequences in snoRNAs that may enhance rRNA methylation efficiency.
• To elucidate the structural organization and protein interactions within box C/D snoRNPs.

Main Methods:

• Bioinformatic analysis of over 2000 yeast and human box C/D snoRNAs.
• RNA-protein crosslinking experiments in Saccharomyces cerevisiae.
• In vivo rRNA methylation assays.

Main Results:

• Identification of conserved sequences in snoRNAs that form 'extra base-pairing' with rRNA regions adjacent to the methylation site.
• Demonstration that this extra base-pairing can increase methylation efficiency by up to five-fold.
• Characterization of divergent box C'/D' motifs bound by snoRNP proteins, confirming their activity in rRNA methylation.

Conclusions:

• The study highlights the significant role of extended snoRNA-rRNA interactions in boosting methylation efficiency.
• Evidence suggests non-catalytic snoRNP subunits (Nop56, Nop58) are involved in rRNA binding.
• Findings support an asymmetric model for box C/D snoRNP organization and provide deeper understanding of snoRNP structure-function relationships.