title: NAB1 is an RNA binding protein involved in the light-regulated differential expression of the light-harvesting antenna of Chlamydomonas reinhardtii.
abstract: Photosynthetic organisms respond to changes in ambient light by modulating the size and composition of their light-harvesting complexes, which in the case of the green alga Chlamydomonas reinhardtii consists of >15 members of a large extended family of chlorophyll binding subunits. How their expression is coordinated is unclear. Here, we describe the analysis of an insertion mutant, state transitions mutant3 (stm3), which we show has increased levels of LHCBM subunits associated with the light-harvesting antenna of photosystem II. The mutated nuclear gene in stm3 encodes the RNA binding protein NAB1 (for putative nucleic acid binding protein). In vitro and in vivo RNA binding and protein expression studies have confirmed that NAB1 differentially binds to LHCBM mRNA in a subpolysomal high molecular weight RNA-protein complex. Binding of NAB1 stabilizes LHCBM mRNA at the preinitiation level via sequestration and thereby represses translation. The specificity and affinity of binding are determined by an RNA sequence motif similar to that used by the Xenopus laevis translation repressor FRGY2, which is conserved to varying degrees in the LHCBM gene family. We conclude from our results that NAB1 plays an important role in controlling the expression of the light-harvesting antenna of photosystem II at the posttranscriptional level. The similarity of NAB1 and FRGY2 of Xenopus implies the existence of similar RNA-masking systems in animals and plants.
authors.affiliation: Department of Biology/Molecular Cell Physiology, University of Bielefeld, Germany.
authors.forename: Jan H
authors.initials: JH
authors.lastname: Mussgnug
authors.forename: Lutz
authors.initials: L
authors.lastname: Wobbe
authors.forename: Ingolf
authors.initials: I
authors.lastname: Elles
authors.forename: Christina
authors.initials: C
authors.lastname: Claus
authors.forename: Mary
authors.initials: M
authors.lastname: Hamilton
authors.forename: Andreas
authors.initials: A
authors.lastname: Fink
authors.forename: Uwe
authors.initials: U
authors.lastname: Kahmann
authors.forename: Aliki
authors.initials: A
authors.lastname: Kapazoglou
authors.forename: Conrad W
authors.initials: CW
authors.lastname: Mullineaux
authors.forename: Michael
authors.initials: M
authors.lastname: Hippler
authors.forename: Jörg
authors.initials: J
authors.lastname: Nickelsen
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Nixon
authors.forename: Olaf
authors.initials: O
authors.lastname: Kruse
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism; D018076:DNA, Complementary; D004591:Electrophoresis, Polyacrylamide Gel; D005453:Fluorescence; D015870:Gene Expression; D047468:Immunoprecipitation; D045342:Light-Harvesting Protein Complexes / Q000235:genetics*; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D018076:DNA, Complementary; D045342:Light-Harvesting Protein Complexes; D010940:Plant Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D002734:Chlorophyll