title: Purification of a site-specific endonuclease, I-Sce II, encoded by intron 4 alpha of the mitochondrial coxI gene of Saccharomyces cerevisiae.
abstract: We have purified to near homogeneity a site-specific, double-stranded DNA endonuclease (I-Sce II) encoded by intron 4 alpha (aI4 alpha) of the yeast mitochondrial coxI gene. Our purification starts with a high salt extract of mitochondria isolated from a yeast strain that overproduces the enzyme because of a block in splicing of aI4 alpha. The final step of purification is an affinity column consisting of covalently bound double-stranded DNA multimers of a synthetic sequence, 5'-TTGGTCATCCAGAAGTAT-3', which contains the I-Sce II cleavage/recognition site. Typical yields of enzyme are 3-5% with a specific activity of approximately 500,000 units/mg, where 1 unit of activity cleaves 50 ng of DNA substrate/h at 30 degrees C. I-Sce II has a monomer molecular mass of 31 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Active enzyme purifies as a 55-kDa species, which we presume to be a homodimer. I-Sce II monomer comigrates with an in vivo synthesized mitochondrial translation product made in the strain that overproduces the enzyme. We conclude that I-Sce II is derived by proteolytic processing of a precursor polypeptide, p62, encoded by an in-frame fusion of coxI exons 1-4 with the downstream aI4 alpha reading frame. I-Sce II is most active at pH 7.5 and at 20-30 degrees C. Endonuclease activity is sensitive to salt and is dependent upon Mg2+ or Mn2+, but is unaffected by inclusion of ATP or GTP. I-Sce II is the first intron-encoded protein to be purified and characterized from yeast mitochondria.
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235.
authors.forename: C M
authors.initials: CM
authors.lastname: Wernette
authors.forename: R
authors.initials: R
authors.lastname: Saldahna
authors.forename: P S
authors.initials: PS
authors.lastname: Perlman
authors.forename: R A
authors.initials: RA
authors.lastname: Butow
mesh_terms: D001483:Base Sequence; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004272:DNA, Mitochondrial / Q000235:genetics*; D015252:Deoxyribonucleases, Type II Site-Specific; D003576:Electron Transport Complex IV / Q000235:genetics*; D004706:Endodeoxyribonucleases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D005800:Genes, Fungal; D007438:Introns; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009838:Oligodeoxyribonucleotides; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D013379:Substrate Specificity
chemical_list: D004272:DNA, Mitochondrial; D009838:Oligodeoxyribonucleotides; D029701:Saccharomyces cerevisiae Proteins; D003576:Electron Transport Complex IV; D004706:Endodeoxyribonucleases; C066166:AI4 protein, S cerevisiae; D015252:Deoxyribonucleases, Type II Site-Specific