Absence of F1-ATPase activity in Kluyveromyces lactis lacking the ε subunit

The mitochondrial F-1-ATPase is a multimeric enzyme, comprised of 3 alpha, 3 beta, gamma, delta and epsilon subunits. that is primarily responsible for the synthesis of ATP in eukaryotic cells. Recent work has shown that the F-1 complex of the petite-negative yeast kluyveromyces lactis, with specific mutations in the alpha, beta or gamma subunits, has a novel function that suppresses lethality caused by loss of mtDNA. Previously, genes for the four largest subunits of K. lactis F-1 have been identified and characterised. In this study the gene coding for the c-subunit of Fl(1) KlATP epsilon, has been isolated and found to encode a polypeptide of 61 amino acids with only 32 residues identical to those in the protein from Saccharomyces cerevisiae. Strains carrying a null mutation of KlATP epsilon respiratory deficient while the introduction of ATP epsilon: from S. cervisiae restores growth on non-fermentable carbon sources. In contrast to S. cerevisiae, K. lactis disrupted in ATP epsilon does not have a detectable F-1-related mitochondrial ATP hydrolysis activity, suggesting that the epsilon-subunit plays a critical role in the formation of the catalytic sector of F-1. With a disrupted KlATP epsilon, the rho degrees-lethality suppressor function of F-1 carrying the atp2-1 and atp1-6 alleles is abolished. However, inactivation of the epsilon subunit does not eliminate the rho degrees-viable phenotype of the atp-1, atp2-9, atp3-2 mutants. It is suggested that the absence of epsilon may effect the assembly or stability of F-1 in the wild-type, atp 2-1 and atp1-6 strains, whereas the defect can be suppressed by the atp1-1, atp2-9 and atp3-2 mutations in the alpha, beta and gamma subunits respectively.