title: The C-terminal kinase and ERK-binding domains of Drosophila S6KII (RSK) are required for phosphorylation of the protein and modulation of circadian behavior.
abstract: A detailed structure/function analysis of Drosophila p90 ribosomal S6 kinase (S6KII) or its mammalian homolog RSK has not been performed in the context of neuronal plasticity or behavior. We previously reported that S6KII is required for normal circadian periodicity. Here we report a site-directed mutagenesis of S6KII and analysis of mutants, in vivo, that identifies functional domains and phosphorylation sites critical for the regulation of circadian period. We demonstrate, for the first time, a role for the S6KII C-terminal kinase that is independent of its known role in activation of the N-terminal kinase. Both S6KII C-terminal kinase activity and its ERK-binding domain are required for wild-type circadian period and normal phosphorylation status of the protein. In contrast, the N-terminal kinase of S6KII is dispensable for modulation of circadian period and normal phosphorylation of the protein. We also show that particular sites of S6KII phosphorylation, Ser-515 and Thr-732, are essential for normal circadian behavior. Surprisingly, the phosphorylation of S6KII residues, in vivo, does not follow a strict sequential pattern, as implied by certain cell-based studies of mammalian RSK protein.
authors.affiliation: Department of Neuroscience, Center for Neuroscience Research, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Tangredi
authors.forename: Fanny S
authors.initials: FS
authors.lastname: Ng
authors.forename: F Rob
authors.initials: FR
authors.lastname: Jackson
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D057906:Circadian Clocks / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010766:Phosphorylation / Q000235:genetics; D017434:Protein Structure, Tertiary; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3