Cain, Amanda Jane; (1998) A study of the molecular biology of the small subunits of photosystem two. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Photosystem two is a multi subunit protein complex which carries out a photochemical reaction producing reduced plastoquinone and molecular oxygen as the products. The proteins which form this centre are encoded for by both nuclear and chloroplast genes and while the function of some has been determined, many play an unknown role. This thesis will discuss mutants created in the subunits PSII-H and PSII-N, the isolation and sequencing of the psbW gene in C.reinhardtii and the characterisation of the conserved gene ycf9. The first chapter discusses the creation of a series of mutants in genes of the psbB operon. The psbH deletion mutants gave a PSII minus phenotype and were unable to grow photoautotrophically. In comparison PSII-N minus cells were capable of photosynthetic growth but appeared to be more susceptible to high light damage. The role of the phosphorylatable threonine of PSII-H was also addressed by the creation of a site directed mutation at this position. The resulting data from the analysis of this mutant did not explain the reason for this characteristic. The next chapter begins with the screening of a series of nuclear PSII mutants, with the aim of discovering new nuclear factors controlling the expression of chloroplast PSII genes. This leads into the creation of deletion mutants for the conserved gene ycf9, introduced into both C. reinhardtii and Synechocystis sp PCC 6803. Analysis of these mutants does not lead to a simple hypothesis of the role of this protein as the characteristics from the two organisms are not identical. Further analysis is planned to elucidate the function of the ycf9 protein. The final chapter discusses the nuclear encoded subunit of the PSII core, PSII-W. We report the isolation and partial sequencing of the gene for this protein in C. reinhardtii. Further analysis showed this to be a single copy gene containing two introns, which is expressed as a 1kb transcript. The mature protein sequence showed high similarity to other species over the N-terminal region, with a greater degree of variability in the C-terminal portion.

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