ETIOLATED CELLS OF CHLAMYDOMONAS-REINHARDTII - CHOICE MATERIAL FOR CHARACTERIZATION OF MITOCHONDRIAL-MEMBRANE POLYPEPTIDES

We have investigated a light-conditional mutant of Chlamydomonas reinh ardtii (J12) that is unable to synthesize chlorophyll in the dark with the aim of characterizing the mitochondrial membrane polypeptides of this alga. A crude membrane fraction derived from etiolated cells was analyzed by gel electrophoresis, immunoblot analysis, and pulse-labeli ng in the presence of specific protein synthesis inhibitors, This frac tion contained both mitochondrial and etioplast membranes, and the lat ter contained appreciable amounts of subunits of the cytochrome b(6)f complex. The mitochondria-encoded subunit 1 of cytochrome-c oxidase ca lled COX1 was identified, and its synthesis was detected in this membr ane fraction. The redox-difference spectra of mitochondrial cytochrome s were studied in whole cells and membrane fractions, in both respirat ory-competent and -deficient strains. Mitochondrial membranes could be further purified after sucrose gradient centrifugation, The use of et iolated cells and their membrane extracts, in association with appropr iate methodologies, opens ways to study the molecular genetics of mito chondria in C. reinhardtii and allows us to address the question of th e cooperation established between the three genetic compartments of a plant cell.