SUBSTITUTION OF PIM1 PROTEASE IN MITOCHONDRIA BY ESCHERICHIA-COLI LONPROTEASE

PIM1 protease in mitochondria belongs to a conserved family of ATP-dep endent proteases, which includes the Escherichia coli Lon protease. Ye ast cells lacking PIM1 are largely defective in degrading misfolded pr oteins in the mitochondrial matrix, are respiratory deficient, and los e integrity of mitochondrial DNA. In order to analyze whether E. coli Lon protease is functionally equivalent to mitochondrial PIM1 protease , yeast cells lacking the PIM1 gene were transformed with a construct consisting of a mitochondrial targeting sequence fused onto the Lon pr otease. In these cells, the fusion protein was expressed and imported into mitochondria, and the targeting sequence was removed. In the abse nce of PIM1 protease, the E. coli Lon protease mediated the degradatio n of misfolded proteins in the matrix space in cooperation with the mi tochondrial hsp70 system. These cells maintained the integrity of the mitochondrial genome and the respiratory function at 30 degrees C but not at 37 degrees C. Stabilization of mitochondrial DNA in Delta pim1 cells depended on protein degradation by the E. coli Lon protease, as a proteolytically inactive Lon variant was not capable of substituting for a loss of PIM1 protease. These results demonstrate functional con servation of Lon-like proteases from prokaryotes to eukaryotes and she d new light on the role of Lon-like proteases in mitochondrial biogene sis.