TRANSLOCATION OF PRECYTOCHROME-C(2) INTO INTRACYTOPLASMIC MEMBRANE-VESICLES OF RHODOBACTER-CAPSULATUS REQUIRES A PERIPHERAL MEMBRANE-PROTEIN

Rhodobacter capsulatus is a member of the group of alpha-purple bacteria which are closely related to the ancestral endosymbiont that gave rise to mitochondria. It has therefore been hypothesized that the molecular mechanisms governing protein export in alpha-purple bacteria have been conserved during the evolution of mitochondria. To enable analysis of protein export in alpha-purple bacteria we describe here the development of a homologous cell-free synthesis/export system consisting entirely of components of R. capsulatus. Translocation of precytochrome c2 into intracytoplasmic membrane vesicles of this organism was found to require the proton-motive force and proceed at a significantly higher efficiency when membranes were present during protein synthesis. Furthermore, we show that, in this cell-free system, translocation depends on a preparation of peripheral membrane proteins which do not possess detectable SecA- and SecB-like actvities.