NMR STRUCTURE OF THE BACTERIOPHAGE-LAMBDA N PEPTIDE BOXB RNA COMPLEX - RECOGNITION OF A GNRA FOLD BY AN ARGININE-RICH MOTIF/

The structure of the complex formed by the arginine-rich motif of the transcriptional antitermination protein N of phage lambda and boxB RNA was determined by heteronuclear magnetic resonance spectroscopy. A be nt alpha helix in N recognizes primarily the shape and negatively char ged surface of the boxB hairpin through multiple hydrophobic and ionic interactions. The GAAGA boxB loop forms a GNRA fold, previously descr ibed for tetraloops, which is essential for N binding. The fourth nucl eotide of the loop extrudes from the GNRA fold to enable the E. coli e longation factor NusA to recognize the N protein/RNA complex. This str ucture reveals a new mode of RNA-protein recognition and shows how a s mall RNA element can facilitate a protein-protein interaction and ther eby nucleate formation of a large ribonucleoprotein complex.