An RBD that does not bind RNA: NMR secondary structure determination and biochemical properties of the C-terminal RNA binding domain from the human U1A protein.

We have obtained backbone 1H, 15N, and 13C assignments and determined the secondary structure and folding topology of the C-terminal RNA-binding domain (RBD) of the human U1A protein. The secondary structure derived from NOE data is in excellent agreement with the predicted structure from the 1H and 13C chemical shift indices. This 88 amino acid domain exhibits a beta alpha beta-beta alpha beta folding pattern, with conserved RNP1 and RNP2 sequences located in two adjacent strands of a four-strand antiparallel beta-sheet. This global folding pattern is typical of this class of RNA binding proteins. Although this domain contains residues that are conserved in all RBDs, its RNA binding properties are very unusual. RNA binding studies show that this domain does not bind U1, U2 or U5 snRNA, an RNA hairpin, rA16, rU16, rC16 or rA3U3GUA4, nor does it show significant association to populations of random sequence RNAs.