Mechanistic Analysis of Chromatin Remodeling

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 DESCRIPTION (provided by applicant): The packaging of DNA into chromatin makes it largely inaccessible for the central nuclear processes of transcription, replication, recombination and repair. ATP-dependent chromatin remodeling motors play key roles in both increasing DNA access within chromatin as well in generating higher-order chromatin structures that promote transcriptional repression. However, the mechanisms by which chromatin remodeling motors function are largely unknown. The overall goal of this proposal is to use concepts learnt from well-studied motors such as kinesin and helicases to understand how a major ATP dependent chromatin-remodeling complex, human ACF functions. ACF functions as a dimeric motor to generate evenly spaced nucleosomes. The ordered nucleosome spacing enables higher-order chromatin folding and gene silencing. Our work over the current grant period has led to the unexpected finding that ACF used ATP to induce substantial distortions within an intact histone octamer. We have further found that coordination between the two ATPase protomers within a dimeric ACF relies on specific recognition of nucleosomal cues. Here we will build on these discoveries to address the following fundamental questions: (1) How does ACF use the energy of ATP to distort nucleosome conformation and how is this distortion coupled to nucleosome movement? (2) How are the activities of the two ACF promoters coordinated and how are substrate cues used in this process?