NMR structure of the N-terminal domain of Saccharomyces cerevisiaeRNase HI reveals a fold with a strong resemblance to the N-terminal domain of ribosomal protein L911Edited by P. E. Wright

In addition to the conserved and well-defined RNase H domain, eukaryotic RNases HI possess either one or two copies of a small N-terminal domain. The solution structure of one of the N-terminal domains from Saccharomyces cerevisiaeRNase HI, determined using NMR spectroscopy, is presented. The 46 residue motif comprises a three-stranded antiparallel β-sheet and two short α-helices which pack onto opposite faces of the β-sheet. Conserved residues involved in packing the α-helices onto the β-sheet form the hydrophobic core of the domain. Three highly conserved and solvent exposed residues are implicated in RNA binding, W22, K38 and K39. The β-β-α-β-α topology of the domain differs from the structures of known RNA binding domains such as the double-stranded RNA binding domain (dsRBD), the hnRNP K homology (KH) domain and the RNP motif. However, structural similarities exist between this domain and the N-terminal domain of ribosomal protein L9 which binds to 23 S ribosomal RNA.