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Molecular and Cellular Biology, February 2006, p. 1434-1444, Vol. 26, No. 4
0270-7306/06/$08.00+0 doi:10.1128/MCB.26.4.1434-1444.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, 6701 Szeged, Hungary,1 Department of Zoology and Animal Biology, University of Geneva, CH-1211 Geneva 4, Switzerland,2 Centre for Cellular and Molecular Biology, Hyderabad 500 007, India3
Received 28 April 2005/ Returned for modification 6 August 2005/ Accepted 2 December 2005
Specific targeting of the protein complexes formed by the Polycomb group of proteins is critically required to maintain the inactive state of a group of developmentally regulated genes. Although the role of DNA binding proteins in this process has been well established, it is still not understood how these proteins target the Polycomb complexes specifically to their response elements. Here we show that the grainyhead gene, which encodes a DNA binding protein, interacts with one such Polycomb response element of the bithorax complex. Grainyhead binds to this element in vitro. Moreover, grainyhead interacts genetically with pleiohomeotic in a transgene-based, pairing-dependent silencing assay. Grainyhead also interacts with Pleiohomeotic in vitro, which facilitates the binding of both proteins to their respective target DNAs. Such interactions between two DNA binding proteins could provide the basis for the cooperative assembly of a nucleoprotein complex formed in vitro. Based on these results and the available data, we propose that the role of DNA binding proteins in Polycomb group-dependent silencing could be described by a model very similar to that of an enhanceosome, wherein the unique arrangement of protein-protein interaction modules exposed by the cooperatively interacting DNA binding proteins provides targeting specificity.
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