Studies on the cytochrome b 6 / f complex. I. Characterization of the complex subunits in $Chlamydomonas\ reinhardtii$

Claire Lemaire (1) , Jacqueline Girard-Bascou (1) , Francis-André Wollman (1) , Pierre Bennoun (1)

1 IBPC (FR_550) - Institut de biologie physico-chimique

We have analyzed the heme-associated peroxidase activity in thylakoid membranes from the. green algae $Chlamydomonas\ reinhardtii$ after electrophoresis in the presence of sodium dodecyl sulfate. Besides cytochrome $f$ and cytochrome $b_6$, we observed peroxidase activity in two other bands, of 34 and 11 kDa, of unknown origin. Characterization of the $b_6/f$ complex subunits was undertaken by means of a comparison of the polypeptide deficiencies in several $b_6/f$ mutants with the polypeptide content of preparations enriched in $b_6/f$ complexes. We conclude that the $b_6/f$ complex consists of five subunits. Using site-specific translation inhibitors, we show that cytochrome $f$, cytochrome $b_6$ and subunit IV are of chloroplast origin, whereas the Rieske protein and probably subunit V are translated on cytoplasmic ribosomes. A model of assembly of the complex is proposed: a cytochrome moiety, comprising the subunits of chloroplast origin, is assembled in the thylakoid membranes prior to the insertion and assembly of the subunits encoded in the nuclear genome.

Mots clés: Cytochrome br/f complex; Peroxidase; Thylakoid membrane; Protein assembly; Chloroplast biogenesis

Domaines: Sciences du Vivant [q-bio]

Claire Lemaire, Jacqueline Girard-Bascou, Francis-André Wollman, Pierre Bennoun. Studies on the cytochrome b 6 / f complex. I. Characterization of the complex subunits in $Chlamydomonas\ reinhardtii$. Biochimica biophysica acta (BBA) - Bioenergetics, 1986, 851 (2), pp.229-238. ⟨10.1016/0005-2728(86)90130-1⟩. ⟨cea-02946507⟩