Photoregulation of LHC-II Accumulation in Thylakoids during Chloroplast Development
The biogenesis of the photosynthetic units depends on close cooperation of the chloroplast and cytoplasm protein synthesizing machinery:the reaction center (RC) core proteins are coded by the plastid DNA, synthesized on thylakoid-bound ribosomes, and cotranslationaly inserted into the developing membrane; on the other hand, the light-harvesting antennae apoprotein LHC-II, is coded by nuclear DNA, synthesized on cytoplasmic ribosomes, as higher molecular weight hydrophilic precursor, it is post-translationally imported through the plastid envelope, and after its processing to its mature size, by cleavage of its transient sequence, it is incorporated into the thylakoid. No precursor or mature form have been detected in the envelope or stroma of the chloroplast, suggesting a rapid transport through the various compartments. A small amount of precursor LHC-II apoprotein has been found in the thylakoid recently, suggesting that processing may also take place in the thylakoid1–3. Stabilization of the mature hydrophobic protein in the thylakoid seems to require concomitant Chlorophyll synthesis, which allows its stabilization via Chl-protein complex formation.
KeywordsContinuous Light Unit Formation Unit Content Reaction Center Protein PSII Unit
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