title: Specific recognition of RNA/DNA hybrid and enhancement of human RNase H1 activity by HBD.
abstract: Human RNase H1 contains an N-terminal domain known as dsRHbd for binding both dsRNA and RNA/DNA hybrid. We find that dsRHbd binds preferentially to RNA/DNA hybrids by over 25-fold and rename it as hybrid binding domain (HBD). The crystal structure of HBD complexed with a 12 bp RNA/DNA hybrid reveals that the RNA strand is recognized by a protein loop, which forms hydrogen bonds with the 2'-OH groups. The DNA interface is highly specific and contains polar residues that interact with the phosphate groups and an aromatic patch that appears selective for binding deoxyriboses. HBD is unique relative to non-sequence-specific dsDNA- and dsRNA-binding domains because it does not use positive dipoles of alpha-helices for nucleic acid binding. Characterization of full-length enzymes with defective HBDs indicates that this domain dramatically enhances both the specific activity and processivity of RNase H1. Similar activity enhancement by small substrate-binding domains linked to the catalytic domain likely occurs in other nucleic acid enzymes.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Marcin
authors.initials: M
authors.lastname: Nowotny
authors.forename: Susana M
authors.initials: SM
authors.lastname: Cerritelli
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Ghirlando
authors.forename: Sergei A
authors.initials: SA
authors.lastname: Gaidamakov
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Crouch
authors.forename: Wei
authors.initials: W
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020029:Base Pairing; D018360:Crystallography, X-Ray; D004247:DNA / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009692:Nucleic Acid Heteroduplexes / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism*; D016914:Ribonuclease H / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D009692:Nucleic Acid Heteroduplexes; D012313:RNA; D004247:DNA; D016914:Ribonuclease H; C078856:ribonuclease HI