title: Homing endonuclease I-TevIII: dimerization as a means to a double-strand break.
abstract: Homing endonucleases are unusual enzymes, capable of recognizing lengthy DNA sequences and cleaving site-specifically within genomes. Many homing endonucleases are encoded within group I introns, and such enzymes promote the mobility reactions of these introns. Phage T4 has three group I introns, within the td, nrdB and nrdD genes. The td and nrdD introns are mobile, whereas the nrdB intron is not. Phage RB3 is a close relative of T4 and has a lengthier nrdB intron. Here, we describe I-TevIII, the H-N-H endonuclease encoded by the RB3 nrdB intron. In contrast to previous reports, we demonstrate that this intron is mobile, and that this mobility is dependent on I-TevIII, which generates 2-nt 3' extensions. The enzyme has a distinct catalytic domain, which contains the H-N-H motif, and DNA-binding domain, which contains two zinc fingers required for interaction with the DNA substrate. Most importantly, I-TevIII, unlike the H-N-H endonucleases described so far, makes a double-strand break on the DNA homing site by acting as a dimer. Through deletion analysis, the dimerization interface was mapped to the DNA-binding domain. The unusual propensity of I-TevIII to dimerize to achieve cleavage of both DNA strands underscores the versatility of the H-N-H enzyme family.
authors.affiliation: Wadsworth Center, New York State Department of Health, Center for Medical Science, Albany, NY 12208, USA.
authors.forename: Justin B
authors.initials: JB
authors.lastname: Robbins
authors.forename: Michelle
authors.initials: M
authors.lastname: Stapleton
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Stanger
authors.forename: Dorie
authors.initials: D
authors.lastname: Smith
authors.forename: John T
authors.initials: JT
authors.lastname: Dansereau
authors.forename: Victoria
authors.initials: V
authors.lastname: Derbyshire
authors.forename: Marlene
authors.initials: M
authors.lastname: Belfort
mesh_terms: D017122:Bacteriophage T4 / Q000201:enzymology / Q000235:genetics; D001665:Binding Sites; D002384:Catalysis; D053903:DNA Breaks, Double-Stranded; D004252:DNA Mutational Analysis; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins / Q000737:chemistry; D019281:Dimerization; D004706:Endodeoxyribonucleases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007438:Introns; D017434:Protein Structure, Tertiary; D015032:Zinc / Q000378:metabolism
chemical_list: D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D004706:Endodeoxyribonucleases; D015032:Zinc