CATALYTIC ACTIVITY OF THE YEAST SWI SNF COMPLEX ON RECONSTITUTED NUCLEOSOME ARRAYS/

A novel, quantitative nucleosome array assay has been developed that c ouples the activity of a nucleosome 'remodeling' activity to restricti on endonuclease activity. This assay has been used to determine the ki netic parameters of ATP-dependent nucleosome disruption by the yeast S WI/SNF complex. Our results support a catalytic mode of action for SWI /SNF in the absence of nucleosome targeting. In this quantitative assa y SWI/SNF and ATP lead to a 100-fold increase in nucleosomal DNA acces sibility, and initial rate measurements indicate that the complex can remodel one nucleosome every 4.5 min on an 11mer nucleosome array. In contrast to SWI/SNF action on mononucleosomes, we find that the SWI/SN F remodeling reaction on a nucleosome array is a highly reversible pro cess. This result suggests that recovery from SWI/SNF action involves interactions among nucleosomes. The biophysical properties of model nu cleosome arrays, coupled with the ease with which homogeneous arrays c an be reconstituted and the DNA accessibility analyzed, makes the desc ribed array system generally applicable for functional analysis of oth er nucleosome remodeling enzymes, including histone acetyltransferases .