title: Structural basis for the assembly of the Sxl-Unr translation regulatory complex.
abstract: Genetic equality between males and females is established by chromosome-wide dosage-compensation mechanisms. In the fruitfly Drosophila melanogaster, the dosage-compensation complex promotes twofold hypertranscription of the single male X-chromosome and is silenced in females by inhibition of the translation of msl2, which codes for the limiting component of the dosage-compensation complex. The female-specific protein Sex-lethal (Sxl) recruits Upstream-of-N-ras (Unr) to the 3' untranslated region of msl2 messenger RNA, preventing the engagement of the small ribosomal subunit. Here we report the 2.8 Å crystal structure, NMR and small-angle X-ray and neutron scattering data of the ternary Sxl-Unr-msl2 ribonucleoprotein complex featuring unprecedented intertwined interactions of two Sxl RNA recognition motifs, a Unr cold-shock domain and RNA. Cooperative complex formation is associated with a 1,000-fold increase of RNA binding affinity for the Unr cold-shock domain and involves novel ternary interactions, as well as non-canonical RNA contacts by the α1 helix of Sxl RNA recognition motif 1. Our results suggest that repression of dosage compensation, necessary for female viability, is triggered by specific, cooperative molecular interactions that lock a ribonucleoprotein switch to regulate translation. The structure serves as a paradigm for how a combination of general and widespread RNA binding domains expands the code for specific single-stranded RNA recognition in the regulation of gene expression.
authors.affiliation: 1] Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, DE-85764, Germany [2] Center for Integrated Protein Science Munich at Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Lichtenbergstr. 4, DE-85747 Garching, Germany.
authors.forename: Janosch
authors.initials: J
authors.lastname: Hennig
authors.affiliation: 1] Centre for Genomic Regulation, Gene Regulation, Stem Cells and Cancer Programme, Dr Aiguader 88, 08003 Barcelona, Spain [2] Universisty Pompeu Fabra, Dr Aiguader 88, 08003 Barcelona, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Militti
authors.affiliation: 1] Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, DE-85764, Germany [2] Center for Integrated Protein Science Munich at Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Lichtenbergstr. 4, DE-85747 Garching, Germany.
authors.forename: Grzegorz M
authors.initials: GM
authors.lastname: Popowicz
authors.affiliation: 1] Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, DE-85764, Germany [2] Center for Integrated Protein Science Munich at Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Lichtenbergstr. 4, DE-85747 Garching, Germany.
authors.forename: Iren
authors.initials: I
authors.lastname: Wang
authors.affiliation: 1] Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, DE-85764, Germany [2] Center for Integrated Protein Science Munich at Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Lichtenbergstr. 4, DE-85747 Garching, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Sonntag
authors.affiliation: Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, DE-85764, Germany.
authors.forename: Arie
authors.initials: A
authors.lastname: Geerlof
authors.affiliation: 1] Université Grenoble Alpes, Institut de Biologie Structurale, F-38044 Grenoble, France [2] Centre National de la Recherche Scientifique, Institut de Biologie Structurale, F-38044 Grenoble, France [3] Commissariat à l'Energie Atomique et aux Energies Alternatives, Institut de Biologie Structurale, F-38044 Grenoble, France [4] Institut Laue-Langevin, F-38042 Grenoble, France.
authors.forename: Frank
authors.initials: F
authors.lastname: Gabel
authors.affiliation: 1] Centre for Genomic Regulation, Gene Regulation, Stem Cells and Cancer Programme, Dr Aiguader 88, 08003 Barcelona, Spain [2] Universisty Pompeu Fabra, Dr Aiguader 88, 08003 Barcelona, Spain.
authors.forename: Fátima
authors.initials: F
authors.lastname: Gebauer
authors.affiliation: 1] Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, DE-85764, Germany [2] Center for Integrated Protein Science Munich at Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Lichtenbergstr. 4, DE-85747 Garching, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Sattler
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D058639:Cold-Shock Response; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D004303:Dosage Compensation, Genetic; D029721:Drosophila Proteins / Q000737:chemistry* / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000737:chemistry* / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation; D008297:Male; D008958:Models, Molecular; D033363:Neutron Diffraction; D019906:Nuclear Magnetic Resonance, Biomolecular; D059372:Nucleotide Motifs; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism; D053838:Scattering, Small Angle; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; C067777:Sxl protein, Drosophila; C509278:UNR protein, Drosophila