The Function of Low Molecular-Weight Polypeptides in Photosystem II

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Photosystem II contains at least 10 polypeptides, approximately 50% of the total number of known plant photosystem II polypeptides, with molecular weights of under 10,000 whose function is mostly unknown. Some have been shown to be encoded by small open reading frames in chloroplast DNA. Still other small open reading frames encode putative membrane polypeptides speculated to be additional photosystem III components. The aim of the proposal is to use techniques of specific mutagenesis to delete the complementary genes from the cyanobacterial chromosome. Because of the similarity of photosystem II complexes from plants ad cyanobacteria this will provide a rapid method to assess the function of the small polypeptides in photosystem II. Site directed mutagenesis will then be used to determine the role of specific amino acids, or specific regions of the polypeptides, in photosystem II assembly and function. Antisera will be raised against synthetic polypeptides matching the products of the open reading frames and used to identify the products in plant photosystem II core preparations. The impact of mutations on photosystem II function and assembly will be studied using a range of techniques including chlorophyll fluorescence emission spectroscopy, oxygen polarography, rapid absorption spectroscopy, and western and northern blotting.