Gemin5-snRNA interaction reveals an RNA binding function for WD repeat domains

Gemin5 binds specifically to the small nuclear RNA (snRNA)-defining small nuclear ribonucleoprotein (snRNP) code sequence and is essential, together with other components of the survival of motor neurons (SMN) complex, for the biogenesis of snRNPs, the major constituents of spliceosomes. We show that this binding is mediated by Gemin5's WD repeat domain, a common domain not previously known to bind RNA independently. The entire WD repeat domain, comprising 13 WD motifs, is both necessary and sufficient for sequence-specific, high-affinity binding of Gemin5 to its RNA targets. Using an RNA-mediated hydroxyl radical probing method and mass spectrometry, we mapped a discrete region of the WD repeat domain that contacts snRNAs and demonstrated by mutagenesis that specific amino acids in this region are crucial for Gemin5-snRNA binding. The WD repeat domain is thus a previously undescribed RNA binding domain, and we suggest that the presence of WD repeats should be considered as predictive of potential function in RNA binding.