A 'loop recapture' mechanism for ACF-dependent nucleosome remodeling

Nat Struct Mol Biol. 2005 Aug;12(8):683-90. doi: 10.1038/nsmb966. Epub 2005 Jul 17.

Abstract

The ATPase ISWI is the molecular motor of several nucleosome remodeling complexes including ACF. We analyzed the ACF-nucleosome interactions and determined the characteristics of ACF-dependent nucleosome remodeling. In contrast to ISWI, ACF interacts symmetrically with DNA entry sites of the nucleosome. Two-color fluorescence cross-correlation spectroscopy measurements show that ACF can bind four DNA duplexes simultaneously in a complex that contains two Acf1 and ISWI molecules. Using bead-bound nucleosomal substrates, nucleosome movement by mechanisms involving DNA twisting was excluded. Furthermore, an ACF-dependent local detachment of DNA from the nucleosome was demonstrated in a novel assay based on the preferred intercalation of ethidium bromide to free DNA. The findings suggest a loop recapture mechanism in which ACF introduces a DNA loop at the nucleosomal entry site that propagates over the histone octamer surface and leads to nucleosome repositioning.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / metabolism
  • Animals
  • Chromatin Assembly and Disassembly / physiology*
  • DNA / metabolism*
  • DNA Footprinting
  • Drosophila
  • Drosophila Proteins / metabolism*
  • Electrophoretic Mobility Shift Assay
  • Ethidium
  • Histones / metabolism
  • Models, Genetic*
  • Nucleosomes / metabolism*
  • Nucleosomes / physiology
  • Polymerase Chain Reaction
  • Spectrometry, Fluorescence
  • Transcription Factors / metabolism*

Substances

  • Acf protein, Drosophila
  • Drosophila Proteins
  • Histones
  • Nucleosomes
  • Transcription Factors
  • DNA
  • Adenosine Triphosphatases
  • Ethidium