title: Expression, purification, and biochemical characterization of the intron-encoded endonuclease, I-CreII.
abstract: The ORF of the Cr.psbA4 intron of Chlamydomonas reinhardtii mediates efficient intron homing, and contains an H-N-H and possibly a GIY-YIG motif. The ORF was over-expressed in Escherichia coli without non-native amino acids, but was mostly insoluble. However, co-over-expression of E. coli chaperonins GroEL/GroES solubilized approximately 50% of the protein, which was purified by ion-exchange and heparin-affinity chromatography. Biochemical characterization showed that the protein is a double-strand-specific endonuclease that cleaves fused psbA exon 4-exon 5 DNA, and was named I-CreII. I-CreII has a relatively relaxed divalent metal ion requirement (Mg(2+), Mn(2+), Ca(2+), and Fe(2+) supported cleavage), is insensitive to salt <350 mM, and is stabilized by DNA. Cleavage of target DNA occurs close (4 nt on the top strand) to the intron-insertion site, and leaves 2-nt 3'-OH overhangs, similar to GIY-YIG endonucleases. The boundaries of the recognition sequence span approximately 30 bp, and encompass the cleavage and intron-insertion sites. Cleavage of heterologous psbA DNAs indicates the enzyme can tolerate multiple, but not all, substitutions in the recognition site. This work will facilitate further study of this novel endonuclease, which may also find use in site-specific manipulation of chloroplast DNA.
authors.affiliation: Section of Molecular Cell and Developmental Biology, Institute for Cellular and Molecular Biology, School of Biological Sciences, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Hyong-Ha
authors.initials: HH
authors.lastname: Kim
authors.forename: Laura E
authors.initials: LE
authors.lastname: Corina
authors.forename: Jung-Keun
authors.initials: JK
authors.lastname: Suh
authors.forename: David L
authors.initials: DL
authors.lastname: Herrin
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics; D048028:DNA, Algal / Q000235:genetics / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004720:Endonucleases / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007438:Introns / Q000235:genetics; D045332:Photosystem II Protein Complex / Q000235:genetics; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification; D012689:Sequence Homology, Nucleic Acid; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D020418:Algal Proteins; D048028:DNA, Algal; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins; C422369:photosystem II, psbA subunit; D004706:Endodeoxyribonucleases; D004720:Endonucleases