The sites of synthesis of the principal thylakoid membrane polypeptides in Chlamydomonas reinhardtii.

Abstract

The sites of synthesis of the major thylakoid membrane polypeptides have been studied in the green alga Chlamydomonas reinhardtii by pulse labeling of cells with[14C]acetate in the presence of inhibitors specific for chloroplast and cytoplasmic protein synthesis. The labeled membrane polypeptides were separated by an improved method of sodium dodecyl sulfate (SDS) gradient gel electrophoresis, and autoradiographs were made of the dried gels. The results demonstrate that of the 33 polypeptides resolved in the gels, at least nine are made on chloroplast ribosomes. Two of these (polypeptides 2 and 6) are associated with the reaction centers of photosystems I and II. Another polypeptide (polypeptide 5) appears from genetic data to be coded by chloroplast DNA. Experiments with a mutant whose chloroplast ribosomes are resistant to spectinomycin (spr-u-l-6-2) show

Synthesis of polypeptides of the chlorophyll—protein complexes in isolated chloroplasts of Euglena gracilis

“…These results also align with the report that chloramphenicol inhibits the synthesis of 2 major polypeptides in a PS II-active membrane fraction of Chkzmydomonas [22]. Similarly, synthesis of polypeptides 5 and 6, considered to be part of PS II in Chlamydomonas [9], was inhibited by chloramphenicol [23]. To gain insight into the polypeptide composition of CPr, CPa and LHCP, we incubated a gel strip similar to that in fig.lA in 2% SDS for 1.5 h, then at 60°C for 5 min to dissociate the &l-protein complexes.…”

Chlorophyll-proteins of thylakoids from wild-type and mutants of barley (Hordeum vulgare L.)

“…Genetic evidence has indicated that polypeptide 6, and possibly polypeptide 5 of Chlamydom0-nas, are involved in the reaction centre of photosystem II (8). Genetic (8) and inhibitor studies (10) have shown that these polypeptides are coded for by chloroplast DNA and are translated on chloroplast ribosomes. Since viridis-m '-9, which lacks Chla-P2, is a nuclear gene mutant, nuclear DNA is involved in the incorporation of Chla-P2 into the thylakoid membrane.…”

A photosystem I mutant in barley (Hordeum vulgare L.)

“…Employing inhibitors of protein synthesis on cytoplasmic and chloroplastic ribosomes in conjunction with mutants resistant towards these inhibitors, CHUA and GILLHAM (11) have shown that the presence of chlorophyll a-protein 1 in the Chlamydomonas thylakoid membrane is dependent on protein synthesis in both the cytoplasmic and chloroplastic compartments. Whether or not this implies that chlorophyll aprotein l is made up of one chloroplast coded and one nuclear coded polypeptide is presently not known.…”