Synthesis, Transport and Assembly of Chloroplast Proteins

Why should we be interested in chloroplast protein synthesis? There are two answers to this question. The major conceptual challenge in biology at the present time is to unravel the molecular basis of differentiation. The leaf is a highly differentiated tissue because of the presence of chloroplasts. Moreover, chloroplasts are easy to isolate, and contain massive amounts of ribulose bisphosphate carboxylase (or Fraction I protein), which catalyses the initial steps in both photosynthesis and photorespiration. The sheer abundance of this protein makes it ideal for studies on the control of protein synthesis, and it is no accident that the first reported in vitro translation of a specific messenger RNA for a plant enzyme produced the large subunit of Fraction I protein1. The second reason for being interested in chloroplast protein synthesis derives from the fact that chloroplasts represent an extranuclear genetic system. When it is realised that most, if not all, eukaryotic cells possess extranuclear genetic systems, the significance of this aspect of chloroplasts is seen to extend beyond photosynthesis and differentiation.