5] Biogenesis of mitochondrial membrane proteins in neurospora crassa

Abstract

This chapter reviews the biogenesis of enzyme complexes of the mitochondrial inner membrane, such as cytochrome oxidase, cytochrome bc 1 , and ATPase, that depends on a close cooperation of mitochondrial and cytoplasmic protein synthesis. Of the numerous polypeptide subunits, which are present in these enzymes, some are synthesized on mitochondrial ribosomes and some on cytoplasmic ribosomes. It discusses that in Neurospora crassa , both the assembly and the site of synthesis of these subunit polypeptides have been studied by in vivo incorporation of radioactive amino acids. The chapter also reviews pulse-labeling experiments with exponentially growing cells that lead to the detection and identification of free subunits occurring as intermediates in the assembly of the functional enzyme complexes. Incorporation of amino acids in the presence of specific inhibitors of mitochondrial or cytoplasmic ribosomes allowed the identification of the translational origin of the individual subunit polypeptides.