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UBC Theses and Dissertations

The role of the pufX protein in photosynthetic electron transfer Lilburn, Timothy George


The role of the puJX gene product of Rhodobacter capsulatus has been unclear, but deletion of the gene renders the organism incapable of photosynthetic growth on a minimal medium. However, suppressor mutants that are able to grow photosynthetically are readily isolated. Two such suppressor mutants were characterized as to their photosynthetic growth properties, their fluorescence at five different incident light intensities, the integrity of their chromatophores and their abilities to generate a trans-membrane potential. I found that the photosynthetic apparatus in the suppressor mutants was less stable than that of the pseudo-wild type and primary mutant strain and that the suppressor mutants used light energy less efficiently than the pseudo-wild type strain. Therefore, the suppressor strains are more correctly designated partial suppressor mutants. The locations and sequences of the suppressor mutations were determined and both were found to change the second codon of the pufA gene. It is hypothesized that the serine residue encoded by this codon is important in interactions between the B870 antenna complex and other membrane-bound polypeptides. Based on these results and those of other investigators, a model for the role of the PufX protein is put forward in which the PufX protein, in conjunction with the B870 ft polypeptide, is proposed to form a gateway in the light harvesting antenna complex surrounding the reaction center. This gateway would allow the passage of quinones and quinols between the reaction center and the cytochrome blc\ complex.

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