title: Hierarchical recruitment of polycomb group silencing complexes.
abstract: Polycomb group (PcG) proteins maintain the transcriptional silence of target genes through many cycles of cell division. Here, we provide evidence for the sequential binding of PcG proteins at a Polycomb response element (PRE) in proliferating cells in which the sequence-specific DNA binding Pho and Phol proteins directly recruit E(z)-containing complexes, which in turn methylate histone H3 at lysine 27 (H3mK27). This provides a tag that facilitates binding by a Pc-containing complex. In wing imaginal discs, these PcG proteins also are present at discrete locations at or downstream of the promoter of a silenced target gene, Ubx. E(z)-dependent H3mK27 is also present near the Ubx promoter and is needed for Pc binding. The location of E(z)- and Pc-containing complexes downstream of the Ubx transcription start site suggests that they may inhibit transcription by interfering with assembly of the preinitiation complex or by blocking transcription initiation or elongation.
authors.affiliation: Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275, USA.
authors.forename: Liangjun
authors.initials: L
authors.lastname: Wang
authors.forename: J Lesley
authors.initials: JL
authors.lastname: Brown
authors.forename: Ru
authors.initials: R
authors.lastname: Cao
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Judith A
authors.initials: JA
authors.lastname: Kassis
authors.forename: Richard S
authors.initials: RS
authors.lastname: Jones
mesh_terms: D000818:Animals; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D020868:Gene Silencing / Q000502:physiology*; D005809:Genes, Regulator / Q000235:genetics; D006657:Histones / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D046911:Macromolecular Substances; D008745:Methylation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D063150:Polycomb Repressive Complex 1; D063151:Polycomb Repressive Complex 2; D063146:Polycomb-Group Proteins; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D006657:Histones; D018398:Homeodomain Proteins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; C066770:Pc protein, Drosophila; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C066177:Ubx protein, Drosophila; C113295:pho protein, Drosophila; C471858:phol protein, Drosophila; C083329:E(z) protein, Drosophila; D063151:Polycomb Repressive Complex 2; D063150:Polycomb Repressive Complex 1