title: Crystallization and preliminary X-ray studies of I-PpoI: a nuclear, intron-encoded homing endonuclease from Physarum polycephalum.
abstract: The homing endonuclease I-PpoI is encoded by an optional third intron, Pp LSU 3, found in nuclear, extrachromosomal copies of the Physarum polycephalum 26S rRNA gene. This endonuclease promotes the lateral transfer or "homing" of its encoding intron by recognizing and cleaving a partially symmetric, 15 bp homing site in 26S rDNA alleles that lack the Pp LSU 3 intron. The open reading frame encoding I-PpoI has been subcloned, and the endonuclease has been overproduced in E. coli. Purified recombinant I-PpoI has been co-crystallized with a 21 bp homing site DNA duplex. The crystals belong to space group P3(1)21, with unit cell dimensions a = b = 114 A, c = 89 A. The results of initial X-ray diffraction experiments indicate that the asymmetric unit contains an enzyme homodimer and one duplex DNA molecule, and that the unit cell has a specific volume of 3.4 A3/dalton. These experiments also provide strong evidence that I-PpoI contains several bound zinc ions as part of its structure.
authors.affiliation: Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Flick
authors.forename: D
authors.initials: D
authors.lastname: McHugh
authors.forename: J D
authors.initials: JD
authors.lastname: Heath
authors.forename: K M
authors.initials: KM
authors.lastname: Stephens
authors.forename: R J
authors.initials: RJ
authors.lastname: Monnat
authors.forename: B L
authors.initials: BL
authors.lastname: Stoddard
mesh_terms: D000818:Animals; D001483:Base Sequence; D019256:Cadmium Chloride / Q000494:pharmacology; D003460:Crystallization; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000737:chemistry*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D007438:Introns; D009841:Oligonucleotides / Q000737:chemistry; D016839:Physarum polycephalum / Q000201:enzymology*; D011994:Recombinant Proteins / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D015032:Zinc / Q000494:pharmacology
chemical_list: D009841:Oligonucleotides; D011994:Recombinant Proteins; D004247:DNA; D004706:Endodeoxyribonucleases; C064579:I-Ppo endonuclease; D015032:Zinc; D019256:Cadmium Chloride