The crystal structure of the RNA binding domain of the U1 small nuclear
ribonucleoprotein A, which forms part of the ribonucleoprotein complex involved
in the excision of introns, has been solved. It contains a four-stranded beta
sheet and two alpha helices. The highly conserved segments designated RNP1 and
RNP2 lie side by side on the middle two beta strands. U1 RNA binding studies of
mutant proteins suggest that the RNA binds to the four-stranded beta sheet and
to the flexible loops on one end.
