Assembly of F0 in Saccharomyces cerevisiae

Abstract

Respiratory deficient mutants of Saccharomyces cerevisiae have been instrumental in identifying an increasing number of nuclear gene products that promote pre- and post-translational steps of the pathway responsible for biogenesis of the mitochondrial ATP synthase. In this article we have attempted to marshal current information about the functions of such accessory factors and the roles they play in expression and assembly of the mitochondrially encoded subunits of the ATP synthase. We also discuss evidence that the ATP synthase may be built up from three separate modules corresponding to the F1 ATPase, the stator and F0.

Figure 1

The subunit organization of the mitochondrial ATP synthase. F₁ is composed of subunits α, β and the three central stalk subunits γ, δ and ε. The F₀ sector contains the subunit 9 oligomer, subunit 6, subunits 8, f and i/j. The peripheral stalk consists of subunits 4, d, h and OSCP. The rotor is made up of the central stalk and the subunit 9 ring.

Figure 2

Polycistronic transcripts of mitochondrial ATP synthase genes in S. cerevisiae. ATP6 and ATP8 are co-transcribed with COX1, encoding subunit 1 of cytochrome c oxidase and, in some strains, ENS2 that codes for a DNA endonuclease. The 5.2 and 4.6 kb mRNAs result from cuts at L and S, respectively. ATP9 is co-transcribed with tRNA^ser and VAR1, encoding a subunit protein of mitochondrial ribosomes. Transcription initiation sites are designated by horizontal arrows. Cleavage sites of the polycistronic transcripts that produce the mature messengers are shown by asterisks.

Figure 3

Assembly of subunit 6 with Atp9 ring is dependent on nuclear encoded accessory proteins (see text for description).

Figure 4

Mechanism of suppression of an atp22 null mutant by a ρ^- genome in which the ATP6 coding sequence was fused to the 5′-UTR, the first exon and the entire first intron of the COX1 gene (see text for description).