title: Pleiohomeotic can link polycomb to DNA and mediate transcriptional repression.
abstract: Polycomb group (PcG) proteins function through cis-acting DNA elements called PcG response elements (PREs) to stably silence developmental regulators, including the homeotic genes. However, the mechanism by which they are targeted to PREs remains largely unclear. Pleiohomeotic (PHO) is a sequence-specific DNA-binding PcG protein and therefore may function to tether other PcG proteins to the DNA. Here, we show that PHO can directly bind to a Polycomb (PC)-containing complex as well as the Brahma (BRM) chromatin-remodeling complex. PHO contacts the BRM complex through its zinc finger DNA-binding domain and a short N-terminal region. A distinct domain of PHO containing a conserved motif contacts the PcG proteins PC and Polyhomeotic (PH). With mobility shift assays and DNA pulldown experiments, we demonstrated that PHO is able to link PC, which lacks sequence-specific DNA-binding activity, to the DNA. Importantly, we found that the PC-binding domain of PHO can mediate transcriptional repression in transfected Drosophila Schneider cells. Concomitant overexpression of PC resulted in stronger PHO-directed repression that was dependent on its PC-binding domain. Together, these results suggest that PHO can contribute to PRE-mediated silencing by direct recruitment of a PC complex to repress transcription.
authors.affiliation: Department of Molecular and Cell Biology, Centre for Biomedical Genetics, Leiden University Medical Center, 2300 RA Leiden, The Netherlands.
authors.forename: Adone
authors.initials: A
authors.lastname: Mohd-Sarip
authors.forename: Francesca
authors.initials: F
authors.lastname: Venturini
authors.forename: Gillian E
authors.initials: GE
authors.lastname: Chalkley
authors.forename: C Peter
authors.initials: CP
authors.lastname: Verrijzer
mesh_terms: D000818:Animals; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000502:physiology*; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism*; D020868:Gene Silencing; D005982:Glutathione Transferase / Q000378:metabolism; D007313:Insecta; D008954:Models, Biological; D063150:Polycomb Repressive Complex 1; D063146:Polycomb-Group Proteins; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; C066770:Pc protein, Drosophila; D063146:Polycomb-Group Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C086469:brm protein, Drosophila; C113295:pho protein, Drosophila; D004247:DNA; D063150:Polycomb Repressive Complex 1; D005982:Glutathione Transferase