The Drosophila Polycomb Group proteins ESC and E(Z) bind directly to each other and co-localize at multiple chromosomal sites.
The Polycomb Group gene esc encodes an evolutionarily conserved protein required for transcriptional silencing of the homeotic genes. Unlike other Polycomb Group genes, esc is expressed and apparently required only during early embryogenesis, suggesting it is required for the initial establishment of silencing but not for its subsequent maintenance. We present evidence that the ESC protein interacts directly with E(Z), another Polycomb Group protein required for silencing of the homeotic genes. We show that the most highly conserved region of ESC, containing seven WD motifs that are predicted to fold into a beta-propeller structure, mediate its binding to a conserved N-terminal region of E(Z). Mutations in the WD region that perturb ESC silencing function in vivo also perturb binding to E(Z) in vitro. The entire WD region forms a trypsin-resistant structure, like known beta -propeller domains, and mutations that would affect the predicted ESC beta-propeller perturb its trypsin-resistance, while a putative structure-conserving mutation does not. We show by co-immunoprecipitation that ESC and E(Z) are directly associated in vivo and that they also co-localize at many chromosomal binding sites. Since E(Z) is required for binding of other Polycomb Group proteins to chromosomes, these results suggest that formation of an E(Z):ESC complex at Polycomb Response Elements may be an essential prerequisite for the establishment of silencing.
Department of Genetics, Case Western Reserve University, Cleveland, Ohio 44106-4955, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002875:Chromosomes / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D017931:DNA Primers / Q000235:genetics; D004330:Drosophila / Q000196:embryology / Q000235:genetics* / Q000378:metabolism*; D029721:Drosophila Proteins; D005801:Genes, Homeobox; D017344:Genes, Insect; D011495:Histone-Lysine N-Methyltransferase; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017354:Point Mutation; D063150:Polycomb Repressive Complex 1; D063151:Polycomb Repressive Complex 2; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D029721:Drosophila Proteins; D019476:Insect Proteins; D009687:Nuclear Proteins; C066770:Pc protein, Drosophila; D012097:Repressor Proteins; C083329:E(z) protein, Drosophila; D011495:Histone-Lysine N-Methyltransferase; D063151:Polycomb Repressive Complex 2; C543389:esc protein, Drosophila; D063150:Polycomb Repressive Complex 1