Chapter 28 - Protein Synthesis in the Chloroplast

Abstract

Translational control functions in diverse biological processes including developmental pattern formation, intracellular protein targeting, the control of homeostasis, and a variety of stress responses. Since the discovery of genomes in plastids, Chlamydomonas research has played a central role in the development of our understanding of the plastid translation machinery and the mechanisms that regulate translation in chloroplasts, and this chapter reviews relevant findings and models. Protein synthesis rates in the Chlamydomonas chloroplast are routinely measured using pulse labeling of intact cells with 35SO4 or [14C] acetate, or isolated chloroplasts with [35S]methionine. This part, radioisotope pulse labeling of newly synthesized proteins, is described under methodologies of protein synthesis. Genetics has been used extensively for the identification and characterization of trans-acting factors and cis-acting sequences that function in the translation of chloroplast mRNAs. Chloroplast ribosomes are introduced and updated with recent research findings. Translation requires general translation factors (GTF), many of which are GTPases activated by the ribosome. The identities and properties of the Chlamydomonas GTFs are covered in this section. Chlamydomonas responds to light in a variety of ways, including changes in chloroplast gene expression at the translational level. This section reviews distinct translational regulatory responses during dark-to-light transitions and under high light stress. Reverse genetic approaches are used to address the functions of other translation factors originally identified through biochemical approaches.