Specificity for the hairy/enhancer of split basic helix-loop-helix (bHLH) proteins maps outside the bHLH domain and suggests two separable modes of transcriptional repression.
The Hairy/Enhancer of split/Deadpan family of basic helix-loop-helix (bHLH) proteins function as transcriptional repressors. We have examined the mechanisms of repression used by the Hairy and E(SPL) proteins by assaying the antagonism between wild-type or altered Hairy/E(SPL) and Scute bHLH proteins during sex determination in Drosophila melanogaster. Domain swapping and mutagenesis of the Hairy and E(SPL) proteins show that three evolutionarily conserved domains are required for their function: the bHLH, Orange, and WRPW domains. However, the suppression of Scute activity by Hairy does not require the WRPW domain. We show that the Orange domain is an important functional domain that confers specificity among members of the Hairy/E(SPL) family. In addition, we show that a Xenopus Hairy homology conserves not only Hairy's structure but also its biological activity in our assays. We propose that transcriptional repression by the Hairy/E(SPL) family of bHLH proteins involves two separable mechanisms: repression of specific transcriptional activators, such as Scute, through the bHLH and Orange domains and repression of other activators via interaction of the C-terminal WRPW motif with corepressors, such as the Groucho protein.
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA.
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Dawson
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Turner
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Weintraub
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Parkhurst
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D051792:Basic Helix-Loop-Helix Proteins; D005075:Biological Evolution; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D004742:Enhancer Elements, Genetic; D005260:Female; D005786:Gene Expression Regulation; D005838:Genotype; D018257:Helix-Loop-Helix Motifs; D007301:Insect Hormones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019476:Insect Proteins; D008297:Male; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012097:Repressor Proteins; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D012732:Sex Determination Analysis; D013379:Substrate Specificity; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D007301:Insect Hormones; D019476:Insect Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C084530:E(spl)mdelta-HLH protein, Drosophila; C489235:hairy protein, Drosophila; C061841:hairy protein, insect