An investigation of the small polypeptides of photosystem II

Photosystem II catalyses the light-driven electron transfer from water to plastoquinone. At present the complex is thought to contain at least 25 different polypeptides. In eukaryotes the components of PSII are encoded for both chloroplast and nuclear genes. Whilst information on the structure of the PSII complex is beginning to emerge, the role that the majority of the subunits play remains unknown. This thesis investigates three of these subunits, the nuclear-encoded subunit PSII-W, the chloroplast-encoded subunit PSII-M and PSII-Z (previously the hypothetical chloroplast protein Ycf9). The gene that encodes the PSII-W protein has been cloned and sequenced from the photosynthetic alga Chlamydomonas reinhardtii. Analysis of the derived amino acid sequence has enabled the characterisation of the PSII-W protein. Antibodies to the mature form of the protein have been raised and used to perform initial expression analysis for the protein and to examine claims that the protein may also be present in a second thylakoid membrane complex, photosystem I. We establish that the PSII-W protein is located exclusively in the PSII complex of C. reinhardtii. Further work has been undertaken to clone and sequence the psbW gene from the moss Physcomitrella patens. Disruption and deletion mutants in the psbZ (previously ycf9) and psbM genes of the cyanobacterium Synechocystis sp. PCC 6803 respectively, have been created by using the kanamycin resistance cassette as a selectable marker. Analysis of these mutants has been undertaken in an attempt to determine the role that each of the proteins plays in the PSII complex. Whilst no definitive role for either of the subunits is established a number of possible functions are ruled out