In Vitro Processing of Precursors of Thylakoid Membrane Proteins of Chlamydomonas reinhardtii y-1

Abstract

Studies of in vitro processing of precursors of the major chlorophyll a/b-binding polypeptides of Chlamydomonas reinhardtii y-1 were undertaken to define the precursor-product relationships. Analysis of translates, prepared from C. reinhardtii poly(A)-rich RNA in a rabbit reticulocyte lysate system, which were incubated with the soluble fraction from C. reinhardtii cells, showed that the 31,500 relative molecular mass (Mr) precursor was converted to the Mr 29,500 thylakoid membrane polypeptide whereas the Mr 30,000 precursor was converted to the Mr 26,000 product. Furthermore, the Mr 31,500 polypeptide, when bound to antibodies, was not processed to the mature polypeptide of Mr 29,500, although the presence of antibodies did not prevent the precursor of Mr 30,000 from being converted to the mature Mr 26,000 polypeptide. The mature fraction of Mr 26,000, was separated into two bands corresponding to polypeptides 16 and 17 in the electrophoretic system of Chua and Bennoun (1975 Proc Natl Acad Sci USA 72: 2175-2179). Processing activity was present in the soluble fraction obtained from cells grown in the light or in the dark. Therefore, processing of the precursor polypeptides does not appear to be involved in the regulation by light of the accumulation of these polypeptides in thylakoid membranes.