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TheSCO2299gene fromStreptomyces coelicolorencodes a single peptide consisting of 497 amino acid residues. Its N-terminal region shows high amino acid sequence similarity to RNase HI, whereas its C-terminal region bears similarity to the CobC protein, which is involved in the synthesis of cobalamin. The SCO2299gene suppressed a temperature-sensitive growth defect of anEscherichia coliRNase H-deficient strain, and the recombinant SCO2299 protein cleaved an RNA strand of RNAÆDNA hybridin vitro. | iFEBS Journal The SCO2299 gene from Streptomyces coelicolor A3 2 encodes a bifunctional enzyme consisting of an RNase H domain and an acid phosphatase domain Naoto Ohtani1 Natsumi Saito1 Masaru Tomita1 Mitsuhiro Itaya1 2 and Aya Itoh1 1 Institute for Advanced Biosciences Keio University Tsuruoka Yamagata Japan 2 Mitsubishi Kagaku Institute of Life Sciences Machida Tokyo Japan Correspondence N. Ohtani Institute for Advanced Biosciences Keio University Tsuruoka Yamagata 997-0017 Japan Tel Fax 81 6 6608 3777 E-mail nao10_oh@ybb.ne.jp Received 12 February 2005 revised 29 March 2005 accepted 5 April 2005 doi 10.1111 j.1742-4658.2005.04704.x The SCO2299 gene from Streptomyces coelicolor encodes a single peptide consisting of 497 amino acid residues. Its N-terminal region shows high amino acid sequence similarity to RNase HI whereas its C-terminal region bears similarity to the CobC protein which is involved in the synthesis of cobalamin. The SCO2299 gene suppressed a temperature-sensitive growth defect of an Escherichia coli RNase H-deficient strain and the recombinant SCO2299 protein cleaved an RNA strand of RNA-DNA hybrid in vitro. The N-terminal domain of the SCO2299 protein when overproduced independently exhibited RNase H activity at a similar level to the full length protein. On the other hand the C-terminal domain showed no CobC-like activity but an acid phosphatase activity. The full length protein also exhibited acid phosphatase activity at almost the same level as the C-terminal domain alone. These results indicate that RNase H and acid phosphatase activities of the full length SCO2299 protein depend on its N-terminal and C-terminal domains respectively. The physiological functions of the SCO2299 gene and the relation between RNase H and acid phosphatase remain to be determined. However the bifunctional enzyme examined here is a novel style in the Type 1 RNase H family. Additionally S. coelicolor is the first example of an organism whose genome contains three .