Chapter 14 Genetics and synthesis of chloroplast membrane proteins

Abstract

Publisher Summary This chapter discusses genetics and synthesis of chloroplast membrane proteins. Photosystem II appears to be the most complicated of the complexes of the thylakoid membrane, both in structure and in regulation of the synthesis of the individual components. The complex may, superficially, be regarded as made up of three assemblies of polypeptides, a light-harvesting complex (LHC II), a core complex, containing primary electron donor P-680, and an oxygen-evolving complex. Oxygen-evolving PS II preparations may be prepared from thylakoid membranes by detergent fractionation or by mechanical fragmentation followed by partition in an aqueous polymer two-phase system. The polypeptides of the oxygen-evolving complex may be separated from the core complex by a variety of salt treatments. The polypeptides of the light-harvesting complex are most easily resolved by polyacrylamide gel electrophoresis of thylakoid membranes solubilized with sodium or lithium dodecyl sulphate. This produces the green chlorophyll-protein band, CP II, which on staining for protein reveals up to four polypeptides of 24–27 kDa, each of which is believed to bind Chl a and Chl b. In most plants, two polypeptides predominate but other minor polypeptides may be resolved. Furthermore, the genes for the polypeptides of the PS II complexes are distributed between the nuclear and chloroplast genomes in higher plants. The only nuclear genes to be characterized to date are those for the polypeptides of LHC II. Although the mature LflC IT polypeptides are relatively highly conserved, there is considerable variability in the amino acid sequence of the transit peptide.