title: GAGA facilitates binding of Pleiohomeotic to a chromatinized Polycomb response element.
abstract: Polycomb response elements (PREs) are chromosomal elements, typically comprising thousands of base pairs of poorly defined sequences that confer the maintenance of gene expression patterns by Polycomb group (PcG) repressors and trithorax group (trxG) activators. Genetic studies have indicated a synergistic requirement for the trxG protein GAGA and the PcG protein Pleiohomeotic (PHO) in silencing at several PREs. However, the molecular basis of this cooperation remains unknown. Here, using DNaseI footprinting analysis, we provide a high-resolution map of sites for the sequence- specific DNA-binding PcG protein PHO, trxG proteins GAGA and Zeste and the gap protein Hunchback (HB) on the 1.6 kb Ultrabithorax (Ubx) PRE. Although these binding elements are present throughout the PRE, they display clear patterns of clustering, suggestive of functional collaboration at the level of PRE binding. We found that while GAGA could efficiently bind to a chromatinized PRE, PHO alone was incapable of binding to chromatin. However, PHO binding to chromatin, but not naked DNA, was strongly facilitated by GAGA, indicating interdependence between GAGA and PHO already at the level of PRE binding. These results provide a biochemical explanation for the in vivo cooperation between GAGA and PHO and suggest that PRE function involves the integrated activities of genetically antagonistic trxG and PcG proteins.
authors.affiliation: Department of Molecular and Cell Biology, Center for Biomedical Genetics, Leiden University Medical Center, PO Box 9503, 2300 RA, Leiden, The Netherlands.
authors.forename: Tokameh
authors.initials: T
authors.lastname: Mahmoudi
authors.forename: Lobke M P
authors.initials: LM
authors.lastname: Zuijderduijn
authors.forename: Adone
authors.initials: A
authors.lastname: Mohd-Sarip
authors.forename: C Peter
authors.initials: CP
authors.lastname: Verrijzer
mesh_terms: D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D063150:Polycomb Repressive Complex 1; D011485:Protein Binding; D020218:Response Elements / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D002843:Chromatin; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; C066770:Pc protein, Drosophila; D014157:Transcription Factors; C063460:Trl protein, Drosophila; C066177:Ubx protein, Drosophila; C060849:z protein, Drosophila; D063150:Polycomb Repressive Complex 1