Function and Assembly of the Accessory Subunits of Photosystem I

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Photosystem I (PS I), the light-dependent plastocyanin- ferredoxin oxidoreductase, is a photosynthetic multisubunit pigment-protein complex in the thylakoid membranes of chloroplasts and cyanobacteria. All cofactors and electron transfer centers in PS I are associated with three polypeptides; the role of the accessory polypeptides, (2) study of the requirements and mechanism of assembly of these accessory subunits into PS I complex. The most feasible approach to achieve the first objective involves molecular cloning and characterization of the genes encoding these polypeptides in the naturally transformable cyanobacterium Synechocystis sp. PCC 6803 and then generating mutants specifically lacking these genes by targeted mutagenesis. Biochemical and spectroscopic analyses of PS I from these mutants will be conducted to assess the effects of loss of individual accessory polypeptides on the assembly and function of PS I. In vitro reconstitution systems will be used to identify the physiological requirements for the assembly of these polypeptides into PS I and to determine the sequence of their assembly. %%% Plants, green algae and cyanobacteria convert light energy into chemical energy with the evolution of molecular oxygen by the process of photosynthesis. Oxygenic photosynthesis is the major source of biological energy and oxygen on this planet and a better understanding of this process is essential for facing the food and environmental challenges of the future.