title: The Caulobacter crescentus CgtAC protein cosediments with the free 50S ribosomal subunit.
abstract: The Obg family of GTPases is widely conserved and predicted to play an as-yet-unknown role in translation. Recent reports provide circumstantial evidence that both eukaryotic and prokaryotic Obg proteins are associated with the large ribosomal subunit. Here we provide direct evidence that the Caulobacter crescentus CgtA(C) protein is associated with the free large (50S) ribosomal subunit but not with 70S monosomes or with translating ribosomes. In contrast to the Bacillus subtilis and Escherichia coli proteins, CgtA(C) does not fractionate in a large complex by gel filtration, indicating a moderately weak association with the 50S subunit. Moreover, binding of CgtA(C) to the 50S particle is sensitive to salt concentration and buffer composition but not guanine nucleotide occupancy of CgtA(C). Assays of epitope-tagged wild-type and mutant variants of CgtA(C) indicate that the C terminus of CgtA(C) is critical for 50S association. Interestingly, the addition of a C-terminal epitope tag also affected the ability of various cgtA(C) alleles to function in vivo. Depletion of CgtA(C) led to perturbations in the polysome profile, raising the possibility that CgtA(C) is involved in ribosome assembly or stability.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Lin
authors.forename: Desiree A
authors.initials: DA
authors.lastname: Thayer
authors.forename: Janine R
authors.initials: JR
authors.lastname: Maddock
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D001426:Bacterial Proteins; D016935:Caulobacter crescentus / Q000737:chemistry*; D002850:Chromatography, Gel; D029968:Escherichia coli Proteins; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry* / Q000502:physiology; D012270:Ribosomes / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D000643:Ammonium Chloride; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; C108621:CgtA protein, bacteria; C491572:ObgE protein, E coli; D020559:Monomeric GTP-Binding Proteins