Formation of oxygen-evolving system of photosynthesis

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Photosynthetic oxygen-evolving system is organized by the coordinated assembly of the nuclear- and chloroplast-encoded proteins in thylakoid membranes under illumination. In the present study, we investigated synthesis and assembly of the PS-II related proteins in the greening process of Euglena cells and barley seedlings. In Euglena, the antenna chlorophyll-binding proteins CP43/47 are unstable in the early stage of greening, and we found that binding of extrinsic 30 kDa proteins to PS II is responsible for the stabilization of CP43/47. The results suggest that the extrinsic 30 kDa proteins are located closely to the antenna chlorophyll-protein complexes and regulates their conformation.We also studied transport of the 30 kDa protein in Euglena cells. To see the structure of the precursor to the 30 kDa protein, we carried out cDNA cloning of the protein. The precursor had a presequence different from that of the corresponding protein from higher plants. Contact sites of the envelope of chloroplasts, which are responsible for translocation of the precursor proteins across the envelopes, were examined by electron microscopy. It is probable that transport of nuclear-encoded proteins in chloroplasts is limited by the envelopes consisting of triple membranes.