Dimerization of doublesex is mediated by a cryptic ubiquitin-associated domain fold: implications for sex-specific gene regulation.
Male- and female-specific isoforms of the Doublesex (DSX) transcription factor regulate somatic sexual differentiation in Drosophila. The isoforms (DSX(M) and DSX(F)) share an N-terminal DNA binding domain (the DM motif), broadly conserved among metazoan sex-determining pathways. DM-DNA recognition is enhanced by a C-terminal dimerization domain. The crystal structure of this domain, determined at a resolution of 1.6 A, reveals a novel dimeric arrangement of ubiquitin-associated (UBA) folds. Although this alpha-helical motif is well characterized in pathways of DNA repair and subcellular trafficking, to our knowledge this is its first report in a transcription factor. Dimerization is mediated by a non-canonical hydrophobic interface extrinsic to the putative ubiquitin binding surface. Key side chains at this interface, identified by alanine scanning mutagenesis, are conserved among DSX homologs. The mechanism of dimerization is thus unrelated to the low affinity domain swapping observed among ubiquitin-associated CUE domains. The unexpected observation of a ubiquitin-associated fold in DSX extends the repertoire of alpha-helical dimerization elements in transcription factors. The possibility that the ubiquitination machinery participates in the regulation of sexual dimorphism is discussed.
Bayrer
James R
JR
Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
Zhang
Wei
W
Weiss
Michael A
MA
D000409:Alanine / Q000737:chemistry; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000737:chemistry*; D019281:Dimerization; D029721:Drosophila Proteins / Q000737:chemistry*; D004331:Drosophila melanogaster; D004583:Electrons; D005260:Female; D005786:Gene Expression Regulation; D006860:Hydrogen Bonding; D008297:Male; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D017510:Protein Folding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012737:Sex Factors; D014157:Transcription Factors / Q000737:chemistry; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000737:chemistry*
D004268:DNA-Binding Proteins; C070369:DSX protein, Drosophila; D029721:Drosophila Proteins; D020033:Protein Isoforms; D014157:Transcription Factors; D025801:Ubiquitin; D004247:DNA; D000409:Alanine