Ultrastructural and biochemical characterization of a Synechocystis 6803 mutant with inactivated psbA genes.
A constructed Synechocystis 6803 mutant with a deletion of the three psbA genes was subjected to ultrastructural and biochemical characterization. This D1-depleted mutant also lacks the D2 protein and the chlorophyll a-binding protein CP-47. A general ultrastructural comparison between the wild type and the mutant did not reveal any major changes in cell appearance. We found by freeze-fracture analysis that approximately 60% of the endoplasmic face particles found in the wild-type thylakoids were missing in the mutant. A corresponding increase in protoplasmic face particles in the mutant thylakoids may represent a subcomplex of those photosystem II (PS II) polypeptides which accumulate in the absence of the D1 protein. Correlation of the PS I:PS II ratio with freeze-fracture data indicates that there is only one reaction center in each PS II freeze-fracture particle. Fluorescence measurements show that the CP-43 polypeptide in the mutant binds chlorophyll and that it may be connected to the phycobilisomes. Excitation energy can be transferred from the phycobilisomes to photosystem I in the absence of the photosystem II reaction center heterodimer and CP-47. This suggests that exciton transfer to photosystem I is mediated either directly by a terminal phycobilisome transmitter or via CP-43.
Nilsson
F
F
Department of Biochemistry, Arrhenius Laboratories, Stockholm University, Sweden.
Simpson
D J
DJ
Jansson
C
C
Andersson
B
B
D001426:Bacterial Proteins / Q000235:genetics*; D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D005614:Freeze Fracturing; D005798:Genes, Bacterial; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D045342:Light-Harvesting Protein Complexes; D008854:Microscopy, Electron; D009154:Mutation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics*; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes; D013050:Spectrometry, Fluorescence
D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes