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Histone Replacement Marks the Boundaries of cis-Regulatory Domains
Yoshiko Mito,1,2Jorja G. Henikoff,1Steven Henikoff1,3*
Cellular memory is maintained at homeotic genes by cis-regulatoryelements whose mechanism of action is unknown. We have examinedchromatin at Drosophila homeotic gene clusters by measuring,at high resolution, levels of histone replacement and nucleosomeoccupancy. Homeotic gene clusters display conspicuous peaksof histone replacement at boundaries of cis-regulatory domainssuperimposed over broad regions of low replacement. Peaks ofhistone replacement closely correspond to nuclease-hypersensitivesites, binding sites for Polycomb and trithorax group proteins,and sites of nucleosome depletion. Our results suggest the existenceof a continuous process that disrupts nucleosomes and maintainsaccessibility of cis-regulatory elements.
1 Basic Sciences Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA. 2 Molecular and Cellular Biology Program, University of Washington, Seattle, WA 98195, USA. 3 Howard Hughes Medical Institute, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
* To whom correspondence should be addressed. E-mail: steveh{at}fhcrc.org
