title: Chloroplast envelope proteins are encoded by the chloroplast genome of Chlamydomonas reinhardtii.
abstract: To characterize envelope proteins encoded by the chloroplast genome, envelopes were isolated from Chlamydomonas reinhardtii cells labeled with [35S] sulfate while blocking synthesis by cytoplasmic ribosomes. One and two-dimensional gel electrophoresis of envelopes and fluorography revealed four highly labeled proteins. Two with masses of 29 and 30 kDa and pI 5.5 were absent from the stroma and thylakoid fractions, while the others at 54 kDa, pI 5.2 and 61 kDa, pI 5.4 were detected there in smaller amounts. The 29- and 30-kDa proteins were associated with outer envelope membranes separated from inner envelope membranes after chloroplast lysis in hypertonic solution. A 32-kDa protein not labeled by [35S]sulfate was found exclusively in the inner membrane fraction, suggesting the existence of a phosphate translocator in C. reinhardtii. To identify envelope proteins exposed on the chloroplast surface, isolated active chloroplasts were surface-labeled with 125I and lactoperoxidase. The 54-kDa, pI 5.2 protein as well as a protein corresponding to either of the 29- or 30-kDa proteins described above were among the labeled components. These results show that envelope proteins of C. reinhardtii are encoded by the chloroplast genome and two are located on the outer envelope membranes.
authors.affiliation: Theodor Kocher Institute, Berne, Switzerland.
authors.forename: J M
authors.initials: JM
authors.lastname: Clemetson
authors.forename: A
authors.initials: A
authors.lastname: Boschetti
authors.forename: K J
authors.initials: KJ
authors.lastname: Clemetson
mesh_terms: D000818:Animals; D001345:Autoradiography; D016825:Chlamydomonas reinhardtii / Q000235:genetics*; D002736:Chloroplasts / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D007425:Intracellular Membranes / Q000378:metabolism; D007525:Isoelectric Focusing; D008565:Membrane Proteins / Q000235:genetics*; D014176:Protein Biosynthesis; D013462:Sulfur Radioisotopes
chemical_list: D008565:Membrane Proteins; D013462:Sulfur Radioisotopes