title: RNA recognition via the SAM domain of Smaug.
abstract: The Nanos protein gradient in Drosophila, required for proper abdominal segmentation, is generated in part via translational repression of its mRNA by Smaug. We report here the crystal structure of the Smaug RNA binding domain, which shows no sequence homology to any previously characterized RNA binding motif. The structure reveals an unusual makeup in which a SAM domain, a common protein-protein interaction module, is affixed to a pseudo-HEAT repeat analogous topology (PHAT) domain. Unexpectedly, we find through a combination of structural and genetic analysis that it is primarily the SAM domain that interacts specifically with the appropriate nanos mRNA regulatory sequence. Therefore, in addition to their previously characterized roles in protein-protein interactions, some SAM domains play crucial roles in RNA binding.
authors.affiliation: Structural Biology Program, Department of Physiology and Biophysics, Mount Sinai School of Medicine, Box 1677, 1425 Madison Avenue, New York, NY 10029, USA.
authors.forename: Justin B
authors.initials: JB
authors.lastname: Green
authors.forename: Cary D
authors.initials: CD
authors.lastname: Gardner
authors.forename: Robin P
authors.initials: RP
authors.lastname: Wharton
authors.forename: Aneel K
authors.initials: AK
authors.lastname: Aggarwal
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016384:Consensus Sequence; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D004330:Drosophila; D029721:Drosophila Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D029721:Drosophila Proteins; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; C402587:smg protein, Drosophila; D012313:RNA