Structural insight into precursor ribosomal RNA processing by ribonuclease MRP

Adapted to the task at hand RNA-based catalysts perform fundamental tasks in cellular RNA metabolism, especially in eukaryotes, where RNAs are cut by specialized ribonucleoproteins (RNPs) as part of ribosome assembly or messenger RNA regulation or splicing. Both RNA and protein components play a role in shaping how these large catalytic complexes interact with their RNA substrates. Lan et al. determined the cryo–electron microscopy structures of a yeast RNP called ribonuclease MRP both alone and bound to a small RNA substrate. Comparison with the related ribonuclease P revealed differences in both protein and RNA components that enable ribonuclease MRP to recognize substrates with a specific sequence motif, rather than purely recognizing RNA structure as ribonuclease P does. These structures aid in considering how RNPs evolved and why they remain central to eukaryotic RNA processing. Science , this issue p. 656