Evidence for DNA Translocation by the ISWI Chromatin-Remodeling Enzyme

Abstract

The ISWI proteins form the catalytic core of a subset of ATP-dependent chromatin-remodeling activities. Here, we studied the interaction of the ISWI protein with nucleosomal substrates. We found that the ability of nucleic acids to bind and stimulate the ATPase activity of ISWI depends on length. We also found that ISWI is able to displace triplex-forming oligonucleotides efficiently when they are introduced at sites close to a nucleosome but successively less efficiently 30 to 60 bp from its edge. The ability of ISWI to direct triplex displacement was specifically impeded by the introduction of 5- or 10-bp gaps in the 3′-5′ strand between the triplex and the nucleosome. In combination, these observations suggest that ISWI is a 3′-5′-strand-specific, ATP-dependent DNA translocase that may be capable of forcing DNA over the surface of nucleosomes.

ACKNOWLEDGMENTS

We thank Brad Cairns, Michael Bruno, Kristina Havas, Nicola Wiechens, Chantal Rencurel, and members of the Division of Gene Regulation and Expression for advice and support.

This work was funded by a Wellcome Trust Senior Research Fellowship (064414), Human Frontiers Programme grant, and an EMBO young investigator award to T.O.-H., a Wellcome Trust 4-year studentship to C.S., and a Wellcome Trust Career Development fellowship (053856) to M.D.S.

I.W. and C.S. contributed equally to this work.