Identification of a nuclear gene (FMC1) required for the assembly/stability of yeast mitochondrial F-1-ATPase in heat stress conditions

We have identified a yeast nuclear gene (FMC1) that is required at elevated temperatures (37 degreesC) for the formation/stability of the F-1 sector o f the mitochondrial ATP synthase, Western blot analysis showed that Fmc1p i s a soluble protein located in the mitochondrial matrix. At elevated temper atures in yeast cells lacking Fmc1p, the alpha -F-1 and beta -F-1 proteins are synthesized, transported, and processed to their mature size. However, instead of being incorporated into a functional F-1 oligomer, they form lar ge aggregates in the mitochondrial matrix. Identical perturbations were rep orted previously for yeast cells lacking either Atp12p or Atp11p, two speci fic assembly factors of the F-1 sector (Ackerman, S, H,, and Tzagoloff, A. (1990) Proc. Natl, Acad, Sci. U.S.A. 87, 4986-4990), and we show that the a bsence of Fmc1p can be efficiently compensated for by increasing the expres sion of Atp12p, However, unlike Atp12p and Atp11p, Fmc1p is not required in normal growth conditions (28-30 degreesC). We propose that Fmc1p is requir ed for the proper folding/stability or functioning of Atp12p in heat stress conditions.