The core histone N-terminal domains are required for multiple rounds of catalytic chromatin remodeling by the SWI/SNF and RSC complexes

SWI/SNF and RSC are large, distinct multi-subunit complexes that use the en ergy of ATP hydrolysis to disrupt nucleosome structure, facilitating the bi nding of transcription factors or restriction enzymes to nucleosomes [Cote, J., Quinn, J., Workman, J. L., and Peterson, C. L. (1994) Science 265, 53- 60 (1); Lorch, Y., Cairns, B. R., Zhang, M., and Kornberg, R. D. (1998) Cel l 94, 29-34 (2)]. Here we have used a quantitative assay to measure the act ivities of these ATP-dependent chromatin remodeling complexes using nucleos omal arrays reconstituted with hypoacetylated, hyperacetylated, or partiall y trypsinized histones. This assay is based on measuring the kinetics of re striction enzyme digestion of a site located within the central nucleosome of a positioned Il-mer array [Logie, C., and Peterson, C. L. (1997) EMBO J. 16, 6772-6782 (3)]. We find that the DNA-stimulated ATPase activities of S WI/SNF and RSC are not altered by the absence of the histone N-termini. Fur thermore, ATP-dependent nucleosome remodeling is also equivalent on all thr ee substrate arrays under reaction conditions where the concentrations of n ucleosomal array and either SWI/SNF or RSC are equivalent. However, SWI/SNF and RSC cannot catalytically remodel multiple nucleosomal arrays in the ab sence of the histone termini, and this catalytic activity of SWI/SNF is dec reased by histone hyperacetylation. These results indicate that the histone termini are important for SWI/SNF and RSC function; and, furthermore, our data defines a step in the remodeling cycle where the core histone termini exert their influence. This step appears to be after remodeling, but prior to intermolecular transfer of the remodelers to new arrays.