title: Low processivity for DNA translocation by the ISWI molecular motor.
abstract: The motor protein ISWI (Imitation SWItch) is the conserved catalytic ATPase domain of the ISWI family of chromatin remodelers. Members of the ISWI family are involved in regulating the structure of cellular chromatin during times of transcription, translation, and repair. Current models for the nucleosome repositioning activity of ISWI and other chromatin remodelers require the translocation of the remodeling protein along double-stranded DNA through an ATP-dependent mechanism. Here we report results from spectrofluorometric stopped-flow experiments which demonstrate that ISWI displays very low processivity for free DNA translocation. By combining these results with those from experiments monitoring the DNA stimulated ATPase activity of ISWI we further demonstrate that the DNA translocation by ISWI is tightly coupled to ATP hydrolysis. The calculated coupling efficiency of 0.067±0.018 ATP/ISWI/bp is seemingly quite low in comparison to similar DNA translocases and we present potential models to account for this. Nevertheless, the tight coupling of ATP hydrolysis to DNA translocation suggests that DNA translocation is not energetically rate limiting for nucleosome repositioning by ISWI.
authors.affiliation: Department of Physics and Astronomy, University of Kansas, 1082 Malott Hall, 1251 Wescoe Hall Dr., Lawrence, KS 66045, USA.
authors.forename: Allen
authors.initials: A
authors.lastname: Eastlund
authors.affiliation: Department of Molecular Biosciences, University of Kansas, 2034 Haworth Hall, 1200 Sunnyside Avenue, Lawrence, KS, USA.
authors.forename: Gada
authors.initials: G
authors.lastname: Al-Ani
authors.affiliation: Department of Physics and Astronomy, University of Kansas, 1082 Malott Hall, 1251 Wescoe Hall Dr., Lawrence, KS 66045, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Fischer
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D042002:Chromatin Assembly and Disassembly; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008956:Models, Chemical; D009707:Nucleosomes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis; D021381:Protein Transport; D013816:Thermodynamics; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism
chemical_list: C086468:ISWI protein; D009707:Nucleosomes; D014157:Transcription Factors; D029867:Xenopus Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases
keywords: Chromatin; ISWI; Kinetics; Proteins; Remodel; Stopped-flow