pipsqueak encodes a factor essential for sequence-specific targeting of a polycomb group protein complex.
The Polycomb (Pc) group (Pc-G) of repressors is essential for transcriptional silencing of homeotic genes that determine the axial development of metazoan animals. It is generally believed that the multimeric complexes formed by these proteins nucleate certain chromatin structures to silence promoter activity upon binding to Pc-G response elements (PRE). Little is known, however, about the molecular mechanism involved in sequence-specific binding of these complexes. Here, we show that an immunoaffinity-purified Pc protein complex contains a DNA binding activity specific to the (GA)n motif in a PRE from the bithoraxoid region. We found that this activity can be attributed primarily to the large protein isoform encoded by pipsqueak (psq) instead of to the well-characterized GAGA factor. The functional relevance of psq to the silencing mechanism is strongly supported by its synergistic interactions with a subset of Pc-G that cause misexpression of homeotic genes.
Huang
Der-Hwa
DH
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 115, Republic of China. mbdhuang@ccvax.sinica.edu.tw
Chang
Yuh-Long
YL
Yang
Chih-Chao
CC
Pan
I-Ching
IC
King
Balas
B
D000818:Animals; D002843:Chromatin / Q000737:chemistry / Q000648:ultrastructure; D002846:Chromatography, Affinity; D004268:DNA-Binding Proteins / Q000235:genetics; D029721:Drosophila Proteins / Q000235:genetics* / Q000502:physiology*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology*; D020868:Gene Silencing / Q000502:physiology*; D005801:Genes, Homeobox; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000502:physiology; D007814:Larva; D046911:Macromolecular Substances; D008297:Male; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D063150:Polycomb Repressive Complex 1; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology*; D012045:Regulatory Sequences, Nucleic Acid; D012091:Repetitive Sequences, Nucleic Acid; D014157:Transcription Factors / Q000502:physiology
D002843:Chromatin; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; C066770:Pc protein, Drosophila; D020033:Protein Isoforms; D014157:Transcription Factors; C063460:Trl protein, Drosophila; C066177:Ubx protein, Drosophila; C097735:psq protein, Drosophila; D063150:Polycomb Repressive Complex 1