Structural mechanisms of RNA recognition: sequence-specific and non-specific RNA-binding proteins and the Cas9-RNA-DNA complex.

RNA-binding proteins play crucial roles in RNA processing and function as regulators of gene expression. Recent studies have defined the structural basis for RNA recognition by diverse RNA-binding motifs. While many RNA-binding proteins recognize RNA sequence non-specifically by associating with 5′ or 3′ RNA ends, sequence-specific recognition by RNA-binding proteins is typically achieved by combining multiple modular domains to form complex binding surfaces. In this review, we present examples of structures from different classes of RNA-binding proteins, identify the mechanisms utilized by them to target specific RNAs, and describe structural principles of how protein–protein interactions affect RNA recognition specificity. We also highlight the structural mechanism of sequence-dependent and -independent interactions in the Cas9-RNA-DNA complex.