Studies are proposed which allow the continued characterization of the Photosystem I (PS I) and Photosystem II (PS II) reaction centers via molecular genetics. The roles of several recently cloned genes, including psaC, psaD, psaE, and psbH, will be pursued by interposon and/or site-directed mutagenesis. The primary goal of the proposed work is to establish methods and strains which will allow a detailed analysis of PS I structure and function in Synechococcus sp. PCC 7002. Special attention will be given to the low-molecular-mass polypeptides associated with the PS I and PS II reaction centers. Additional work on the role(s) of light and nutrients in the regulation of cyanobacterial gene expression will be pursued by transcript analyses and gene fusion methods. Finally, we will continue to explore the phylogenetic relationships among cyanobacteria, cyanelles, and chloroplasts.
