title: Site-specific ribonuclease activity of eukaryotic DNA topoisomerase I.
abstract: Type I topoisomerases alter DNA topology by cleaving and rejoining one strand of duplex DNA through a covalent protein-DNA intermediate. Here we show that vaccinia topoisomerase, a eukaryotic type IB enzyme, catalyzes site-specific endoribonucleolytic cleavage of an RNA-containing strand. The RNase reaction occurs via transesterification at the scissile ribonucleotide to form a covalent RNA-3'-phosphoryl-enzyme intermediate, which is then attacked by the vicinal 2' OH of the ribose sugar to yield a free 2', 3' cyclic phosphate product. Introduction of a single ribonucleoside at the scissile phosphate of an otherwise all-DNA substrate suffices to convert the topoisomerase into an endonuclease. Human topoisomerase I also has endoribonuclease activity. These findings suggest potential roles for topoisomerases in RNA processing.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA.
authors.forename: J
authors.initials: J
authors.lastname: Sekiguchi
authors.forename: S
authors.initials: S
authors.lastname: Shuman
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D010710:Phosphates / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism*; D013379:Substrate Specificity / Q000502:physiology; D013936:Thymidine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D014529:Uridine / Q000378:metabolism; D014616:Vaccinia virus / Q000201:enzymology* / Q000235:genetics
chemical_list: D010710:Phosphates; D012333:RNA, Messenger; D014443:Tyrosine; D004247:DNA; D012260:Ribonucleases; D004264:DNA Topoisomerases, Type I; D013936:Thymidine; D014529:Uridine