RNA-protein complexes.

The three commonly found RNA-binding domains, the ribonucleoprotein (RNP) domain, the double stranded RNA binding domain (dsRBD) and the K homology (KH) domain, have now been shown to have an alpha/beta fold similar to that found in many ribosomal proteins. Crystal structures of two hairpin RNA-protein complexes have been determined recently: the U1A spliceosomal protein bound to hairpin II of U1 small nuclear RNA, and MS2 bacteriophage capsid protein bound to a hairpin present at the ribosomal binding site of MS2 replicase mRNA. The crystal structure of the tryptophan operon RNA binding attenuation protein from Bacillus subtilis shows a novel structure with 11 monomers arranged in a doughnut-shaped ring that binds 11 copies of (U/G)AG triplets presented in the leader sequence of the tryptophan operon polycistronic message.