The Drosophila trithorax protein is a coactivator required to prevent re-establishment of polycomb silencing.
Polycomb group (PcG) and Trithorax (TRX) complexes assemble at Polycomb response elements (PREs) and maintain respectively the repressed and active state of homeotic genes. Although PcG and TRX complexes are distinct, their binding to some PRE fragments in vitro depends on GAGA motifs. GAGA factor immunoprecipitates with both complexes. In presence of a PRE, TRX stimulates expression and prevents the return of repression at later stages. When TRX levels are reduced, repression is re-established in inappropriate regions of imaginal discs, suggesting that TRX insufficiency impairs the epigenetic memory of the active state. Targeting a GAL-TRX fusion shows that TRX is a coactivator that stimulates expression of an active gene but cannot initiate expression by itself. Targeting a histone acetylase to a PRE does not affect embryonic silencing but causes a loss of memory in imaginal discs, suggesting that deacetylation is required to establish the memory of the repressed state.
Poux
Sylvain
S
Department of Zoology, University of Geneva, 30 quai Ernest Ansermet, CH-1211 Geneva, Switzerland.
Horard
Béatrice
B
Sigrist
Christian J A
CJ
Pirrotta
Vincenzo
V
D000107:Acetylation; D000818:Animals; D001665:Binding Sites; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics*; D004625:Embryo, Nonmammalian; D005260:Female; D018507:Gene Expression Regulation, Developmental; D020868:Gene Silencing; D051548:Histone Acetyltransferases; D006657:Histones / Q000378:metabolism; D018398:Homeodomain Proteins; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D063150:Polycomb Repressive Complex 1; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D051548:Histone Acetyltransferases; D006657:Histones; D018398:Homeodomain Proteins; D019476:Insect Proteins; D063150:Polycomb Repressive Complex 1; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor; C066770:Pc protein, Drosophila; C063460:Trl protein, Drosophila; C066177:Ubx protein, Drosophila