title: Intertwined structure of the DNA-binding domain of intron endonuclease I-TevI with its substrate.
abstract: I-TevI is a site-specific, sequence-tolerant intron endonuclease. The crystal structure of the DNA-binding domain of I-TevI complexed with the 20 bp primary binding region of its DNA target reveals an unusually extended structure composed of three subdomains: a Zn finger, an elongated segment containing a minor groove-binding alpha-helix, and a helix-turn-helix. The protein wraps around the DNA, mostly following the minor groove, contacting the phosphate backbone along the full length of the duplex. Surprisingly, while the minor groove-binding helix and the helix-turn- helix subdomain make hydrophobic contacts, the few base-specific hydrogen bonds occur in segments that lack secondary structure and flank the intron insertion site. The multiple base-specific interactions over a long segment of the substrate are consistent with the observed high site specificity in spite of sequence tolerance, while the modular composition of the domain is pertinent to the evolution of homing endonucleases.
authors.affiliation: Wadsworth Center, PO Box 509, Albany, NY 12201-0509, USA. vanroey@wadsworth.org
authors.forename: P
authors.initials: P
authors.lastname: Van Roey
authors.forename: C A
authors.initials: CA
authors.lastname: Waddling
authors.forename: K M
authors.initials: KM
authors.lastname: Fox
authors.forename: M
authors.initials: M
authors.lastname: Belfort
authors.forename: V
authors.initials: V
authors.lastname: Derbyshire
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000737:chemistry / Q000378:metabolism*; D019143:Evolution, Molecular; D018257:Helix-Loop-Helix Motifs; D006860:Hydrogen Bonding; D011487:Protein Conformation; D013379:Substrate Specificity; D016335:Zinc Fingers
chemical_list: D004247:DNA; D004706:Endodeoxyribonucleases; C065074:I-TEVI endonuclease