Crystal structure of the U1A spliceosomal protein complexed with its cognate RNA hairpin.

We have determined the crystal structure of the RNA binding domain of the U1A spliceosomal protein bound to a 21-nucleotide RNA hairpin at 1.92 A resolution. The ten-nucleotide RNA loop binds to the surface of the four-stranded beta-sheet of the RNP domain as an open structure. The AUUGCAC hexanucleotide sequence interacts extensively with the conserved RNP1 and RNP2 motifs and the C-terminal extension of the RNP domain. The stacking interaction between RNA bases and aromatic protein side chains and the extensive hydrogen bonding network involving RNA bases, protein side chains and protein mainchain amide and carbonyl groups are crucial for the sequence specific recognition of RNA.