Structure determination of large biological RNAs.

Complex RNA structures regulate many biological processes but are often too large for structure determination by nuclear magnetic resonance (NMR) methods. We determined the solution structure of domain II of the hepatitis C viral internal ribosome entry site (HCV IRES), a 25-kDa RNA, using a novel NMR approach. Conventional short-range, distance, and torsion angle NMR restraints were combined with long-range, angular restraints derived from residual dipolar couplings (RDCs) to improve both the local and global precision of the structure. This powerful approach should be generally applicable to the NMR structure determination of large, modular RNAs.