CRYSTAL-STRUCTURE OF A NEW RNA-BINDING DOMAIN FROM THE ANTITERMINATORPROTEIN SACY OF BACILLUS-SUBTILIS

SacY belongs to a family of, at present, seven bacterial transcription al antiterminators. The RNA-binding and antitermination capacity of Sa cY resides in the 55 amino acids at the N-terminal [SacY(1-55)]. The c rystal structure at 2 Angstrom resolution shows that SacY(1-55) forms a dimer in the crystal, in accordance with the NMR solution structure, The structure of the monomer is a four-stranded beta-sheet with a sim ple beta 1 beta 2 beta 3 beta 4 topology, One side of the sheet is cov ered by a long surface loop and the other side forms the dimer interfa ce. The dimer is stabilized by the orthogonal stacking of the tyro bet a-sheets, The crystal structure is in excellent agreement with the NMR solution structure (r.m.s. distance for C alpha coordinates is 1.3 An gstrom), The structure of SacY(1-55) reveals a new RNA-binding motif.