title: Structural analysis of the quaking homodimerization interface.
abstract: Quaking (QkI) is a prototypical member of the STAR (signal transducer and activator of RNA) protein family, which plays key roles in posttranscriptional gene regulation by controlling mRNA translation, stability and splicing. QkI-5 has been shown to regulate mRNA expression in the central nervous system, but little is known about its roles in other tissues. STAR proteins function as dimers and bind to bipartite RNA sequences; however, the structural and functional roles of homodimerization and heterodimerization are still unclear. Here, we present the crystal structure of the QkI dimerization domain, which adopts a similar stacked helix-turn-helix arrangement as its homologs GLD-1 (germ line development defective-1) and Sam68 (Src-associated protein during mitosis, 68kDa) but differs by an additional helix inserted in the dimer interface. Variability of the dimer interface residues likely ensures selective homodimerization by preventing association with non-cognate STAR family proteins in the cell. Mutations that inhibit dimerization also significantly impair RNA binding in vitro, alter QkI-5 protein levels and impair QkI function in a splicing assay in vivo. Together, our results indicate that a functional Qua1 homodimerization domain is required for QkI-5 function in mammalian cells.
authors.affiliation: Department of Molecular Biology, Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Beuck
authors.forename: Song
authors.initials: S
authors.lastname: Qu
authors.forename: W Samuel
authors.initials: WS
authors.lastname: Fagg
authors.forename: Manuel
authors.initials: M
authors.lastname: Ares
authors.forename: James R
authors.initials: JR
authors.lastname: Williamson
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017354:Point Mutation; D011487:Protein Conformation; D050791:STAT Transcription Factors / Q000737:chemistry* / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D050791:STAT Transcription Factors