THE FORMATION OF RESPIRATORY-CHAIN COMPLEXES IN MITOCHONDRIA IS UNDERTHE PROTEOLYTIC CONTROL OF THE M-AAA PROTEASE

Yta10p (Afg3p) and Yta12p (Rcal1p), members of the conserved AAA famil y of ATPases, are submits of the mitochondrial m-AAA protease, an inne r membrane ATP-dependent metallopeptidase. Deletion of YTA10 or YTA12 impairs degradation of nonassembled inner membrane proteins and assemb ly of respiratory chain complexes, Mutations of the proteolytic sites in either YTA10 or YTA12 have been shown to inhibit proteolysis of mem brane-integrated polypeptides but not the respiratory competence of th e cells, suggesting additional activities of Yta10p and Yta12p. Here w e demonstrate essential proteolytic functions of the m-AAA protease in the biogenesis of the respiratory chain. Cells harbouring proteolytic ally inactive forms of both Yta10p and Yta12p are respiratory deficien t and exhibit a pleiotropic phenotype similar to Delta yta10 and Delta yta12 cells, They show deficiencies in expression of the intron-conta ining mitochondrial genes COX1 and COB, Splicing of COX1 and COB trans cripts is impaired in mitochondria lacking m-AAA protease, whilst tran scription and translation can proceed in the absence of Yta10p or Yta1 2p, The function of the m-AAA protease appears to be confined to intro ns encoding mRNA maturases. Our results reveal an overlapping substrat e specificity of the subunits of the m-AAA protease and explain the im paired assembly of respiratory chain complexes by defects in expressio n of intron-containing genes in mitochondria lacking m-AAA protease.