Regulation of Protein Synthesis in Chloroplasts of Chlamydomonas Reinhardii

Abstract

The chloroplast genome contains about 100 genes for proteins. The biogenesis of the chloroplast, however, requires at least 5 to 10 times more protein species. Most of these peptides are encoded in the nuclear genome, synthesized as precursors in the cytoplasm, and transported, while processed, into the chloroplast. Many multimeric protein complexes of the chloro-plast, e.g. Rubisco, PS II-core complexes, ribosomes, are built up stoichiometrically by peptide-subunits from both origins, the cytoplasm and the chloroplast. Since the pool of free subunits in the plastid is usually rather low, a cooperation of the nuclear and chloroplast genetic systems is necessary to keep the synthesis of partner proteins in step and for an efficient synthesis of the holocomplexes. This becomes especially obvious during chloroplast biogenesis or when the enzyme equipment of the plastid has to be adapted to new environmental or developmental conditions. The mechanism of this regulation between the nucleo-cytoplasm and the chloroplast is still unknown.