Trigger Factor and its involvement in the repair of Photosystem II

Replacement of the photosynthetic D1 protein is essential for continuation of photosynthesis and the life of a plant or cyanobacteria. Trigger Factor (TF) is an approximately 52 kDa molecular chaperone which may bind the ribosome-D1 complex prior to the association with the thylakoid targeted Signal Recognition Particle (cpSRP54). Trigger Factor binds to nearly all ribosomes, hence it is feasible that TF binds D1 protein and stalls until cpSRP54 can target it to SecY. The aim of this research was to create a TFSpec mutant of Synechocystis sp. PCC 6803 which would allow the characterisation of the TFSpec phenotype and to characterise the Synechocystis sp. PCC 6803 TF protein. The TFSpec strain showed several physiological differences from Wild Type (WT). The rate of O2 evolution by the TFSpec strain was slower than for the WT strain over the same period, and the growth rates of the TFSpec strain was lower than the WT strain. Trigger Factor was also differentially detected in various cellular fractions when pelleted with ribosomes purified from cells grown under different light con- ditions. Biophysical analysis of TF was done by Circular Dichroism and Dynamic Light Scattering to determine the structural similarity with TF from other species. Crystallisation of TF was also attempted. Implications of this research are discussed