Yeast Isw1p Forms Two Separable Complexes In Vivo

Abstract

There are several classes of ATP-dependent chromatin remodeling complexes, which modulate the structure of chromatin to regulate a variety of cellular processes. The budding yeast, Saccharomyces cerevisiae, encodes two ATPases of the ISWI class, Isw1p and Isw2p. Previously Isw1p was shown to copurify with three other proteins. Here we identify these associated proteins and show that Isw1p forms two separable complexes in vivo (designated Isw1a and Isw1b). Biochemical assays revealed that while both have equivalent nucleosome-stimulated ATPase activities, Isw1a and Isw1b differ in their abilities to bind to DNA and nucleosomal substrates, which possibly accounts for differences in specific activities in nucleosomal spacing and sliding. In vivo, the two Isw1 complexes have overlapping functions in transcriptional regulation of some genes yet distinct functions at others. In addition, these complexes show different contributions to cell growth at elevated temperatures.

ACKNOWLEDGMENTS

We thank Tom Fazzio, Marnie Gelbart, Cedar McKay, and Sue Biggins for helpful discussions. We also thank Bertrand Séraphin for providing us with the plasmid for TAP epitope labeling.

This work was supported by a Pew Charitable Trust Biomedical Scholars fellowship and National Institutes of Health grants GM58465 to T.T., 5T32 HD07183 to J.C.V., CA74841 to C.K., and GM48413 to B.B. In addition, B.B. was supported by the American Cancer Society grant RPG-99-199-01-GMC.