title: The two-step cleavage activity of PI-TfuI intein endonuclease demonstrated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry.
abstract: PI-TfuI, an intein spliced from the DNA polymerase of Thermococcus fumicolans, is a highly specific endonuclease, whose cleavage efficiency and specificity depend on both the substrate topology and the divalent cation used as cofactor. An open circular intermediate was observed during the cleavage of supercoiled DNA by PI-TfuI, suggesting a two-step cleavage of the DNA. We characterized this nicked intermediate and, through the development of a method of analysis of the cleavage reaction based on matrix-assisted laser desorption ionization time-of-flight mass spectrometry, we demonstrated that the cleavage of DNA by PI-TfuI indeed results from two cleavage events. One step results in the cleavage of the bottom strand, which is independent of the DNA conformation or choice of the metal ion cofactor. A second step, which is slower, leads to the cleavage of the top strand and governs the specific requirements of PI-TfuI concerning the essential cofactor and the DNA topology. These two steps were shown to be independent in optimal conditions of cleavage. These data give support to the existence of two distinct and independent active sites in the endonuclease domain of the archaeal intein.
authors.affiliation: Institut de Pharmacologie et Biologie Structurale, I.P.B.S./C.N.R.S., 205 Route de Narbonne, F-31077 Toulouse Cedex, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Thion
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Laurine
authors.forename: Monique
authors.initials: M
authors.lastname: Erard
authors.forename: Odile
authors.initials: O
authors.lastname: Burlet-Schiltz
authors.forename: Bernard
authors.initials: B
authors.lastname: Monsarrat
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Masson
authors.forename: Isabelle
authors.initials: I
authors.lastname: Saves
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence; D004278:DNA, Superhelical / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000737:chemistry* / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D019712:Thermococcus / Q000201:enzymology* / Q000235:genetics
chemical_list: D019843:Archaeal Proteins; D004278:DNA, Superhelical; D009841:Oligonucleotides; D011994:Recombinant Proteins; D008345:Manganese; D004706:Endodeoxyribonucleases; D008274:Magnesium