tailieunhanh - Báo cáo khoa học: Ribonuclease H: molecular diversities, substrate binding domains, and catalytic mechanism of the prokaryotic enzymes

The prokaryotic genomes, for which complete nucleotide sequences are available, always contain at least one RNase H gene, indicating that RNase H is ubiquitous in all prokaryotic cells. Coupled with its unique substrate specificity, the enzyme has been expected to play crucial roles in the biochemical processes associated with DNA replication, gene expression and DNA repair. | MINIREVIEW Ribonuclease H molecular diversities substrate binding domains and catalytic mechanism of the prokaryotic enzymes Takashi Tadokoro and Shigenori Kanaya Department of Materialand Life Science Osaka University Japan Keywords catalytic mechanism crystal structure evolution genome hybrid binding domain molecular diversity prokaryote RNase H RNA DNA hybrid substrate-binding domain Correspondence S. Kanaya Department of Materialand Life Science Graduate Schoolof Engineering Osaka University 2-1 Yamadaoka Suita Osaka 565-0871 Japan Fax Tel 81 6 6879 7938 E-mail kanaya@ Received 18 October 2008 revised 18 December 2008 accepted 12 January 2009 The prokaryotic genomes for which complete nucleotide sequences are available always contain at least one RNase H gene indicating that RNase H is ubiquitous in all prokaryotic cells. Coupled with its unique substrate specificity the enzyme has been expected to play crucial roles in the biochemical processes associated with DNA replication gene expression and DNA repair. The physiological role of prokaryotic RNases H especially of type 1 RNases H has been extensively studied using Escherichia coli strains that are defective in RNase HI activity or overproduce RNase HI. However it is not fully understood yet. By contrast significant progress has been made in this decade in identifying novel RNases H with respect to their biochemical properties and structures and elucidating catalytic mechanism and substrate recognition mechanism of RNase H. We review the results of these studies. doi Identification of bacterial RNase HIII with a TBP-like substrate-binding domain RNase H is defined as an enzyme that specifically hydrolyzes the phosphodiester bonds of RNA hybridized to DNA at the P-O3 bond. Prokaryotic RNases H which are involved in DNA replication repair and transcription 1 2 have been classified into RNases HI HII and HIII based on differences in their amino acid .