Protein Synthesis in Chloroplasts

Abstract

In order to study protein synthesis within chloroplasts it is often necessary to eliminate cytoplasmic protein synthesis. This can be done by two methods:

• a) Specific inhibitors of protein synthesis block translation either on chloroplast 70S ribosomes or on cytoplasmic 80S ribosomes. Using e.g. cycoheximide, radioactive amino acids will be exclusively incorporated in proteins synthesized in the organelles. This method enables the in vivo translation of proteins in chloroplasts (and mitochondria) in whole cells or plants to be studied specifically.

• b) When pure, intact, photosynthetically active chloroplasts are isolated, cytoplasmic protein synthesis is physically removed. Incorporation of amino acids in such chloroplasts is called in organello protein synthesis. As will be shown later, such chloroplasts also form the starting material for homologous in vitro translation systems.