Identification of putative interaction partners for the Xenopus Polycomb-group protein Xeed.
The extra sex combs (esc) gene of Drosophila and its mammalian homologue embryonic ectoderm development (eed) play pivotal roles in establishing Polycomb-group (Pc-G) mediated transcriptional silencing of regulatory genes during early development. We have carried out a two-hybrid screen in yeast to identify maternally expressed proteins that interact directly with the product of the Xenopus eed homologue, Xeed. Xeed-interacting proteins that were recovered in this screen included a maternal Xenopus histone deacetylase (HDACm), the Xeed protein itself, and a Xenopus homologue of Enhancer of zeste (XEZ) - a second member of the Pc-G that is closely related by sequence similarity to histone methyltransferases. We have also identified a novel interaction between Xeed and a component of the Xenopus basal transcription machinery, TAF(II)32. We show for the first time that each of these proteins interacts with the Xeed polypeptide, both in the yeast two-hybrid assay and in vitro using purified recombinant proteins. XEZ, HDACm and TAF(II)32 mRNAs are all strongly co-expressed with Xeed mRNA in the fertilized egg, further suggesting that their encoded proteins could interact with Xeed during early embryonic development. Our observations support a multi-step model for the onset of transcriptional silencing in which Xeed binds to and inhibits the function of the transcription initiation complex and also recruits proteins that mediate the acquisition by associated chromatin of epigenetically heritable, post-translational modifications.
Showell
Christopher
C
Centre for Developmental Genetics, School of Medicine and Biomedical Science, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK.
Cunliffe
Vincent T
VT
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D004625:Embryo, Nonmammalian / Q000378:metabolism; D047108:Embryonic Development; D000071221:Enhancer of Zeste Homolog 2 Protein; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D063151:Polycomb Repressive Complex 2; D063146:Polycomb-Group Proteins; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D035381:TATA-Binding Protein Associated Factors; D035362:Transcription Factor TFIID; D019473:Transcription Factors, TFII / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism*
D018076:DNA, Complementary; C491487:EED protein, Xenopus; C491488:EED protein, human; D009687:Nuclear Proteins; D063146:Polycomb-Group Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C106849:TAF9 protein, human; D035381:TATA-Binding Protein Associated Factors; D035362:Transcription Factor TFIID; D019473:Transcription Factors, TFII; D029867:Xenopus Proteins; C583224:EZH2 protein, Xenopus; D000071221:Enhancer of Zeste Homolog 2 Protein; D063151:Polycomb Repressive Complex 2; D006655:Histone Deacetylases