RNA-protein complexes regulate gene expression at the level of transcription, mRNA processing, and translation.  Below is a gallery of structures determined in the Williamson laboratory, using NMR spectroscopy or X-ray crystallography (or both!)

HIV Rev-RRE5 complex NMR PDB ID: 1etf (Battiste et al 1996) http://www.rcsb.org/pdb/explore/explore.do?structureId=1etf

HIV Tar-Arginine complex NMR PDB ID: 1aju (Brodsky and Williamson 1997) http://www.rcsb.org/pdb/explore/explore.do?structureId=1aju

Phi 21-N BoxB complex NMR PDB ID: 1nyb (Cilley and Williamson 2003) http://www.rcsb.org/pdb/explore/explore.do?structureId=1nyb

S6 S15 S18 16S complex X-Ray Diffraction PDB ID: 1g1x (Agalarov et al 2000) http://www.rcsb.org/pdb/explore/explore.do?structureId=1g1x

GLD1(Qua1) homodimerization domain X-Ray Diffraction PDB ID: 3KBL (Beuck et al 2010) http://www.rcsb.org/pdb/explore/explore.do?structureId=3KBL

NXF2-NXT1 complex X-Ray Diffraction PDB ID: 3NV0 (Kerkow et al, unpublished) http://www.rcsb.org/pdb/explore/explore.do?structureId=3NV0

SIRV coat protein X-Ray Diffraction PDB ID: 3F2E (Szymczyna et al 2009) http://www.rcsb.org/pdb/explore/explore.do?structureId=3F2E

FHV B2-dsRNA complex X-Ray Diffraction PDB ID: 2az0 (Chao et al 2005) http://www.rcsb.org/pdb/explore/explore.do?structureId=2az0

Yeast L30e-mRNA complex NMR PDB ID: 1ck2 (Mao and Williamson 1999) http://www.rcsb.org/pdb/explore/explore.do?structureId=1ck2