title: Dependency of ISW1a chromatin remodeling on extranucleosomal DNA.
abstract: The nucleosome remodeling activity of ISW1a was dependent on whether ISW1a was bound to one or both extranucleosomal DNAs. ISW1a preferentially bound nucleosomes with an optimal length of approximately 33 to 35 bp of extranucleosomal DNA at both the entry and exit sites over nucleosomes with extranucleosomal DNA at only one entry or exit site. Nucleosomes with extranucleosomal DNA at one of the entry/exit sites were readily remodeled by ISW1a and stimulated the ATPase activity of ISW1a, while conversely, nucleosomes with extranucleosomal DNA at both entry/exit sites were unable either to stimulate the ATPase activity of ISW1a or to be mobilized. DNA footprinting revealed that a major conformational difference between the nucleosomes was the lack of ISW1a binding to nucleosomal DNA two helical turns from the dyad axis in nucleosomes with extranucleosomal DNA at both entry/exit sites. The Ioc3 subunit of ISW1a was found to be the predominant subunit associated with extranucleosomal DNA when ISW1a is bound either to one or to both extranucleosomal DNAs. These two conformations of the ISW1a-nucleosome complex are suggested to be the molecular basis for the nucleosome spacing activity of ISW1a on nucleosomal arrays. ISW1b, the other isoform of ISW1, does not have the same dependency for extranucleosomal DNA as ISW1a and, likewise, is not able to space nucleosomes.
authors.affiliation: Department of Biochemistry and Molecular Biology, Southern Illinois University School of Medicine, 1245 Lincoln Dr., Neckers Bldg. Room 229, Carbondale, IL 62901-4413, USA.
authors.forename: Vamsi K
authors.initials: VK
authors.lastname: Gangaraju
authors.forename: Blaine
authors.initials: B
authors.lastname: Bartholomew
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D020029:Base Pairing / Q000187:drug effects / Q000235:genetics; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004271:DNA, Fungal / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D009707:Nucleosomes / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism
chemical_list: D003432:Cross-Linking Reagents; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C470548:IOC3 protein, S cerevisiae; D009707:Nucleosomes; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; D000251:Adenosine Triphosphatases; C470546:ISW1 protein, S cerevisiae