Papers In Press, published online ahead of print November 22, 2006
J. Biol. Chem, 10.1074/jbc.M609473200
Submitted on October 6, 2006
Revised on November 14, 2006
Accepted on November 20, 2006
Inverted factor access and slow reversion characterize SWI/SNF-altered nucleosome dimers
Natalia P. Ulyanova and Gavin R. Schnitzler
Biochemistry, Tufts University School of Medicine, Boston, MA 02111
Corresponding Author: gavin.schnitzler{at}tufts.edu
Human SWI/SNF is an ATP-dependent chromatin remodeling complex with important functions in activation and repression of cellular genes. Previously, we showed that hSWI/SNF creates structurally-altered dimers from mononucleosome cores. More recently we found that hSWI/SNF also generates abundant structurally-altered dinucleosomes, called altosomes, on polynucleosomal templates. Here, we find that dimers revert to normal nucleosomes at a similar rate as altosomes and can also be cleaved to yield nucleosomal particles with mobilities similar to mononucleosomes. Using these and other shared properties we propose a single model for both types of hSWI/SNF product. In addition, we further characterize the accessibility of altered dimers to transcription factors, and find that the DNA in dimers is most accessible in the middle and least accessible at the ends, directly opposite the profile of normal mononucleosomes. We also find that transcription factor binding can influence the ratio of normal nucleosomes and dimers as hSWI/SNF products. Implications for the interplay between hSWI/SNF products and transcription factors are discussed.