NAB1 is an RNA binding protein involved in the light-regulated differential expression of the light-harvesting antenna of Chlamydomonas reinhardtii.
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.
Mussgnug
Jan H
JH
Department of Biology/Molecular Cell Physiology, University of Bielefeld, Germany.
Wobbe
Lutz
L
Elles
Ingolf
I
Claus
Christina
C
Hamilton
Mary
M
Fink
Andreas
A
Kahmann
Uwe
U
Kapazoglou
Aliki
A
Mullineaux
Conrad W
CW
Hippler
Michael
M
Nickelsen
Jörg
J
Nixon
Peter J
PJ
Kruse
Olaf
O
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
D018076:DNA, Complementary; D045342:Light-Harvesting Protein Complexes; D010940:Plant Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D002734:Chlorophyll