title: Dual Organellar Targeting of Aminoacyl-tRNA Synthetases in Diatoms and Cryptophytes.
abstract: The internal compartmentation of eukaryotic cells not only allows separation of biochemical processes but it also creates the requirement for systems that can selectively transport proteins across the membrane boundaries. Although most proteins function in a single subcellular compartment, many are able to enter two or more compartments, a phenomenon known as dual or multiple targeting. The aminoacyl-tRNA synthetases (aaRSs), which catalyze the ligation of tRNAs to their cognate amino acids, are particularly prone to functioning in multiple subcellular compartments. They are essential for translation, so they are required in every compartment where translation takes place. In diatoms, there are three such compartments, the plastid, the mitochondrion, and the cytosol. In cryptophytes, translation also takes place in the periplastid compartment (PPC), which is the reduced cytoplasm of the plastid's red algal ancestor and which retains a reduced red algal nucleus. We searched the organelle and nuclear genomes of the cryptophyte Guillardia theta and the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana for aaRS genes and found an insufficient number of genes to provide each compartment with a complete set of aaRSs. We therefore inferred, with support from localization predictions, that many aaRSs are dual targeted. We tested four of the predicted dual targeted aaRSs with green fluorescent protein fusion localizations in P. tricornutum and found evidence for dual targeting to the mitochondrion and plastid in P. tricornutum and G. theta, and indications for dual targeting to the PPC and cytosol in G. theta. This is the first report of dual targeting in diatoms or cryptophytes.
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada g.gile@dal.ca.
authors.forename: Gillian H
authors.initials: GH
authors.lastname: Gile
authors.affiliation: LOEWE Centre for Synthetic Microbiology (SYNMIKRO), Philipps University Marburg, Germany Present address: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Moog
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada Program in Integrated Microbial Biodiversity, Canadian Institute for Advanced Research, Toronto, Ontario, Canada.
authors.forename: Claudio H
authors.initials: CH
authors.lastname: Slamovits
authors.affiliation: LOEWE Centre for Synthetic Microbiology (SYNMIKRO), Philipps University Marburg, Germany Laboratory for Cell Biology, Philipps University Marburg, Germany.
authors.forename: Uwe-G
authors.initials: UG
authors.lastname: Maier
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada Program in Integrated Microbial Biodiversity, Canadian Institute for Advanced Research, Toronto, Ontario, Canada.
authors.forename: John M
authors.initials: JM
authors.lastname: Archibald
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000032:analysis / Q000737:chemistry* / Q000235:genetics; D044785:Cryptophyta / Q000201:enzymology* / Q000235:genetics; D017377:Diatoms / Q000201:enzymology* / Q000235:genetics; D008928:Mitochondria / Q000201:enzymology; D008969:Molecular Sequence Data; D018087:Plastids / Q000201:enzymology; D021382:Protein Sorting Signals
chemical_list: D021382:Protein Sorting Signals; D000604:Amino Acyl-tRNA Synthetases
keywords: Guillardia; PPC; Phaeodactylum; pheRS; protein targeting; syfB