A Polycomb group protein complex with sequence-specific DNA-binding and selective methyl-lysine-binding activities.
Polycomb response elements (PREs) are specific cis-regulatory sequences needed for transcriptional repression of HOX and other target genes by Polycomb group (PcG) proteins. Among the many PcG proteins known in Drosophila, Pho is the only sequence-specific DNA-binding protein. To gain insight into the function of Pho, we purified Pho protein complexes from Drosophila embryos and found that Pho exists in two distinct protein assemblies: a Pho-dINO80 complex containing the Drosophila INO80 nucleosome-remodeling complex, and a Pho-repressive complex (PhoRC) containing the uncharacterized gene product dSfmbt. Analysis of PhoRC reveals that dSfmbt is a novel PcG protein that is essential for HOX gene repression in Drosophila. PhoRC is bound at HOX gene PREs in vivo, and this targeting strictly depends on Pho-binding sites. Characterization of dSfmbt protein shows that its MBT repeats have unique discriminatory binding activity for methylated lysine residues in histones H3 and H4; the MBT repeats bind mono- and di-methylated H3-K9 and H4-K20 but fail to interact with these residues if they are unmodified or tri-methylated. Our results establish PhoRC as a novel Drosophila PcG protein complex that combines DNA-targeting activity (Pho) with a unique modified histone-binding activity (dSfmbt). We propose that PRE-tethered PhoRC selectively interacts with methylated histones in the chromatin flanking PREs to maintain a Polycomb-repressed chromatin state.
Klymenko
Tetyana
T
Gene Expression Programme, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.
Papp
Bernadett
B
Fischle
Wolfgang
W
Köcher
Thomas
T
Schelder
Malgorzata
M
Fritsch
Cornelia
C
Wild
Brigitte
B
Wilm
Matthias
M
Müller
Jürg
J
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D002843:Chromatin / Q000502:physiology; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D029721:Drosophila Proteins / Q000302:isolation & purification / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000737:chemistry / Q000378:metabolism; D020868:Gene Silencing; D006657:Histones / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D008239:Lysine / Q000378:metabolism*; D008745:Methylation; D008969:Molecular Sequence Data; D063146:Polycomb-Group Proteins; D011485:Protein Binding; D014157:Transcription Factors / Q000302:isolation & purification / Q000378:metabolism*
D002843:Chromatin; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D006657:Histones; D018398:Homeodomain Proteins; D063146:Polycomb-Group Proteins; D014157:Transcription Factors; C113295:pho protein, Drosophila; D008239:Lysine