title: The bicoid mRNA localization factor Exuperantia is an RNA-binding pseudonuclease.
abstract: Anterior patterning in Drosophila is mediated by the localization of bicoid (bcd) mRNA at the anterior pole of the oocyte. Exuperantia (Exu) is a putative exonuclease (EXO) associated with bcd and required for its localization. We present the crystal structure of Exu, which reveals a dimeric assembly with each monomer consisting of a 3'-5' EXO-like domain and a sterile alpha motif (SAM)-like domain. The catalytic site is degenerate and inactive. Instead, the EXO-like domain mediates dimerization and RNA binding. We show that Exu binds RNA directly in vitro, that the SAM-like domain is required for RNA binding activity and that Exu binds a structured element present in the bcd 3' untranslated region with high affinity. Through structure-guided mutagenesis, we show that Exu dimerization is essential for bcd localization. Our data demonstrate that Exu is a noncanonical RNA-binding protein with EXO-SAM-like domain architecture that interacts with its target RNA as a homodimer.
authors.affiliation: Max Planck Institute for Developmental Biology, Tübingen, Germany.
authors.forename: Daniela
authors.identifier: 0000-0002-5372-9343
authors.initials: D
authors.lastname: Lazzaretti
authors.affiliation: Max Planck Institute for Developmental Biology, Tübingen, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Veith
authors.affiliation: Bioanalytical Mass Spectrometry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.|Bioanalytics, Institute for Clinical Chemistry, University Medical Center Göttingen, Göttingen, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Kramer
authors.affiliation: Max Planck Institute of Biochemistry, Martinsried, Germany.
authors.forename: Claire
authors.initials: C
authors.lastname: Basquin
authors.affiliation: Bioanalytical Mass Spectrometry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.|Bioanalytics, Institute for Clinical Chemistry, University Medical Center Göttingen, Göttingen, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Urlaub
authors.affiliation: Max Planck Institute for Developmental Biology, Tübingen, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Irion
authors.affiliation: Max Planck Institute for Developmental Biology, Tübingen, Germany.
authors.forename: Fulvia
authors.initials: F
authors.lastname: Bono
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D029721:Drosophila Proteins / Q000737:chemistry* / Q000502:physiology; D004331:Drosophila melanogaster / Q000201:enzymology*; D004527:Egg Proteins / Q000737:chemistry* / Q000502:physiology; D005092:Exonucleases / Q000737:chemistry* / Q000502:physiology; D005260:Female; D018398:Homeodomain Proteins / Q000378:metabolism; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D021381:Protein Transport; D012313:RNA / Q000737:chemistry; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D004527:Egg Proteins; D018398:Homeodomain Proteins; D016601:RNA-Binding Proteins; D015534:Trans-Activators; C056478:bcd protein, Drosophila; C072067:exu protein, Drosophila; D012313:RNA; D005092:Exonucleases