title: Identification of RNase HII from psychrotrophic bacterium, Shewanella sp. SIB1 as a high-activity type RNase H.
abstract: The gene encoding RNase HII from the psychrotrophic bacterium, Shewanella sp. SIB1 was cloned, overexpressed in Escherichia coli, and the recombinant protein was purified and biochemically characterized. SIB1 RNase HII is a monomeric protein with 212 amino acid residues and shows an amino acid sequence identity of 64% to E. coli RNase HII. The enzymatic properties of SIB1 RNase HII, such as metal ion preference, pH optimum, and cleavage mode of substrate, were similar to those of E. coli RNase HII. SIB1 RNase HII was less stable than E. coli RNase HII, but the difference was marginal. The half-lives of SIB1 and E. coli RNases HII at 30 degrees C were approximately 30 and 45 min, respectively. The midpoint of the urea denaturation curve and optimum temperature of SIB1 RNase HII were lower than those of E. coli RNase HII by approximately 0.2 M and approximately 5 degrees C, respectively. However, SIB1 RNase HII was much more active than E. coli RNase HII at all temperatures studied. The specific activity of SIB1 RNase HII at 30 degrees C was 20 times that of E. coli RNase HII. Because SIB1 RNase HII was also much more active than SIB1 RNase HI, RNases HI and HII represent low- and high-activity type RNases H, respectively, in SIB1. In contrast, RNases HI and HII represent high- and low-activity type RNases H, respectively, in E. coli. We propose that bacterial cells usually contain low- and high-activity type RNases H, but these types are not correlated with RNase H families.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, Japan.
authors.forename: Hyongi
authors.initials: H
authors.lastname: Chon
authors.forename: Takashi
authors.initials: T
authors.lastname: Tadokoro
authors.forename: Naoto
authors.initials: N
authors.lastname: Ohtani
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Koga
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Takano
authors.forename: Shigenori
authors.initials: S
authors.lastname: Kanaya
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004789:Enzyme Activation; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D016914:Ribonuclease H / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D020592:Shewanella / Q000145:classification* / Q000201:enzymology*; D013045:Species Specificity; D013379:Substrate Specificity; D015854:Up-Regulation
chemical_list: C091139:ribonuclease HII; D016914:Ribonuclease H