title: Targeted interruption of the psaA and psaB genes encoding the reaction-centre proteins of photosystem I in the filamentous cyanobacterium Anabaena variabilis ATCC 29413.
abstract: The two reaction-centre proteins of the photosystem I (PSI) complex are encoded by two adjacent genes named psaA and psaB. We have performed targeted mutagenesis to insertionally inactivate each of these genes in the filamentous cyanobacterium Anabaena variabilis ATCC 29413. The resulting mutant strains, termed psaA::NmR and psaB::NmR, were blue because of a high ratio of phycobilin to chlorophyll and were unable to grow in light. These mutant cells also lacked chemically reducible P700 (the reaction-centre chlorophylls of PSI) and as a consequence did not exhibit any PSI-mediated photochemical activity. However, their photosystem II (PSII) complexes were fully active. The loss of the PsaA and PsaB proteins and their associated chlorophyll molecules resulted in a five- to sevenfold decrease in the chlorophyll/PSII ratio in the mutant cells relative to the wild-type cells. Interestingly, the psaB::NmR and not the psaA::NmR mutant strain retained a small fluorescence peak (77K) at 721 nm originating from chlorophyll molecule(s) presumably bound to a small amount of the PsaA protein present in the psaB mutant. These results demonstrate that this organism is suitable for the manipulation of PSI reaction-centre proteins.
authors.affiliation: Department of Biology, Washington University, St Louis, Missouri 63130-4899.
authors.forename: K J
authors.initials: KJ
authors.lastname: Nyhus
authors.forename: T
authors.initials: T
authors.lastname: Thiel
authors.forename: H B
authors.initials: HB
authors.lastname: Pakrasi
mesh_terms: D017033:Anabaena / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D001205:Ascorbic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D002734:Chlorophyll / Q000378:metabolism; D003001:Cloning, Molecular; D017931:DNA Primers; D004237:Diuron / Q000378:metabolism; D004579:Electron Transport; D004926:Escherichia coli; D005798:Genes, Bacterial; D007425:Intracellular Membranes / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010641:Phenotype; D045322:Photosynthetic Reaction Center Complex Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D045331:Photosystem I Protein Complex; D045524:Phycobilisomes; D010860:Pigments, Biological / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D016133:Polymerase Chain Reaction / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; C073973:PSI-A protein, Synechococcus; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045524:Phycobilisomes; D010860:Pigments, Biological; D010940:Plant Proteins; C089909:photosystem I, psaB subunit; D002734:Chlorophyll; D004237:Diuron; D001205:Ascorbic Acid