Two nuclear mutations that block mitochondrial protein import in yeast.

Abstract

Two yeast mutants that are temperature-sensitive for import of mitochondrial proteins were isolated. Each strain contains a single mutation that results in arrest of growth and accumulation of precursor to the .beta. subunit of the mitochondrial F1-ATPase after incubation at 37.degree. C. These lesions (mas1 and mas2) are nonallelic and recessive. Cells harboring either mutation stop growing only after 2-3 generations at 37.degree. C. Import of the F1 .beta. subunit at 37.degree. C is more than 250 times slower in mas1 and 15 times slower in mas2 than in wild-type cells. At 23.degree. C, import occurs with similar rates in mutant and wild-type cells. The 2 mutations also reduce the rate of import of other proteins; however, import of different pecursors is affected to different degrees in the 2 strains. The temperature-sensitive step in import in both mas1 and mas2 occurs before arrival of precursors in the mitochondrial matrix.