The NblAI protein from the filamentous cyanobacterium Tolypothrix PCC 7601: regulation of its expression and interactions with phycobilisome components.
Cyanobacteria respond to changes in light or nutrient availability by modifications in their photosynthetic light harvesting antenna. In unicellular cyanobacteria a small polypeptide (NblA) is required for phycobilisome degradation following environmental stresses. In the filamentous strain Tolypothrix sp. PCC 7601 the nblAI gene, encoding a NblA homologue, is located upstream of the operon coding for phycoerythrin (cpeBA). The nblAI transcripts all originate from a single transcription start point; their intracellular levels vary according to nitrogen regimes but not with light spectral quality. Using recombinant His-tagged NblAI protein, we found that in vitro NblAI has affinity for both phycocyanin and phycoerythrin subunits from Tolypothrix sp. PCC 7601, but not for allophycocyanin from this cyanobacterium or for phycobiliproteins from other cyanobacterial species. We also observed that although nblAI is mainly expressed under nitrogen starvation, NblAI polypeptides are always present in the cell; a significant portion of them co-purify with phycobilisome preparations but only if cells were grown under red light. Our data indicate that NblAI attaches to the phycobilisomes even under non-inducing conditions and suggest a preferential affinity of NblAI for phycocyanin.
Luque
Ignacio
I
Organismes Photosynthétiques et Environnement, CNRS FRE 2433, Département de Biologie, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Paris Cedex 05, France.
Ochoa De Alda
Jesús A G
JA
Richaud
Catherine
C
Zabulon
Gérald
G
Thomas
Jean-Claude
JC
Houmard
Jean
J
D000220:Adaptation, Biological / Q000502:physiology; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D002874:Chromosome Mapping; D000458:Cyanobacteria / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism; D045524:Phycobilisomes / Q000378:metabolism*; D010798:Phycocyanin / Q000378:metabolism; D010799:Phycoerythrin / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D024363:Transcription Initiation Site; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D002352:Carrier Proteins; D045342:Light-Harvesting Protein Complexes; D045524:Phycobilisomes; D011994:Recombinant Proteins; D010798:Phycocyanin; D010799:Phycoerythrin; D009584:Nitrogen