4c5e
Crystal structure of the minimal Pho-Sfmbt complex (P21 spacegroup)
Structural highlights
FunctionSMBT_DROME Polycomb group (PcG) protein that binds to the Polycomb response elements (PREs) found in the regulatory regions of many genes. PcG proteins act by forming multiprotein complexes, which are required to maintain the transcriptionally repressive state of homeotic genes throughout development. PcG proteins are not required to initiate repression, but to maintain it during later stages of development. They probably act via the methylation of histones, rendering chromatin heritably changed in its expressibility. Necessary but not sufficient to recruit a functional PcG repressive complex that represses target genes, suggesting that the recruitment of the distinct PRC1 complex is also required to allow a subsequent repression.[1] Publication Abstract from PubMedPolycomb group (PcG) protein complexes repress developmental regulator genes by modifying their chromatin. How different PcG proteins assemble into complexes and are recruited to their target genes is poorly understood. Here, we report the crystal structure of the core of the Drosophila PcG protein complex Pleiohomeotic (Pho)-repressive complex (PhoRC), which contains the Polycomb response element (PRE)-binding protein Pho and Sfmbt. The spacer region of Pho, separated from the DNA-binding domain by a long flexible linker, forms a tight complex with the four malignant brain tumor (4MBT) domain of Sfmbt. The highly conserved spacer region of the human Pho ortholog YY1 binds three of the four human 4MBT domain proteins in an analogous manner but with lower affinity. Comparison of the Drosophila Pho:Sfmbt and human YY1:MBTD1 complex structures provides a molecular explanation for the lower affinity of YY1 for human 4MBT domain proteins. Structure-guided mutations that disrupt the interaction between Pho and Sfmbt abolish formation of a ternary Sfmbt:Pho:DNA complex in vitro and repression of developmental regulator genes in Drosophila. PRE tethering of Sfmbt by Pho is therefore essential for Polycomb repression in Drosophila. Our results support a model where DNA tethering of Sfmbt by Pho and multivalent interactions of Sfmbt with histone modifications and other PcG proteins create a hub for PcG protein complex assembly at PREs. Structural basis for targeting the chromatin repressor Sfmbt to Polycomb response elements.,Alfieri C, Gambetta MC, Matos R, Glatt S, Sehr P, Fraterman S, Wilm M, Muller J, Muller CW Genes Dev. 2013 Nov 1;27(21):2367-79. doi: 10.1101/gad.226621.113. PMID:24186981[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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