MUTATIONS ALTERING THE MITOCHONDRIAL-CYTOPLASMIC DISTRIBUTION OF MOD5P IMPLICATE THE ACTIN CYTOSKELETON AND MESSENGER-RNA 3'-ENDS AND OR PROTEIN-SYNTHESIS IN MITOCHONDRIAL DELIVERY/

The Saccharomyces cerevisiae MOD5 gene encodes proteins that function in three subcellular locations: mitochondria, the cytoplasm, and nucle i (M. Boguta, L. A. Hunter, W.-C. Shen, E. C. Gillman, N. C. Martin, a nd A. K. Hopper, Mel. Cell. Biol. 14:2298-2306, 1994; E. C. Gillman, L . B. Slusher, N. C. Martin, and A. K. Hopper, Mel. Cell. Biol. 11:2382 -2390, 1991). A mutant allele of MOD5 encoding a protein (Mod5p-I,KR6) located predominantly in mitochondria was constructed. Mutants defect ive in delivering Mod5p-I,KR6 to mitochondria were sought by selecting cells with increased cytosolic activity of this protein. Twenty-five mutants defining four complementation groups, mdp1, mdp2, mdp3, and md p4, were found. They are unable to respire at 34 degrees C or to grow on glucose medium at 38 degrees C. Cell fractionation studies shelved that mdp1, mdp2, and mdp3 mutants have an altered mitochondrial-cytopl asmic distribution of Mod5p. mdp2 can be suppressed by ACT1, the actin -encoding gene. The actin cytoskeleton organization is also aberrant i n mdp2 cells. MDP2 is the same as VRP1 (S. F. H. Donnelly, M. J. Pickl ington, D. Pallotta, and E. Orr, Mel. Microbiol. 10:585-596, 1993). MD P3 is identical to PAN1, which encodes a protein that interacts with m RNA 3' ends and affects initiation of protein synthesis (A. B. Sachs a nd J. A. Deardoff, Cell 70:961-973, 1992). These results implicate the actin cytoskeleton and mRNA 3' ends and/or protein synthesis as being as important for protein distribution in S. cerevisiae as they are fo r distribution of cytosolic proteins in higher eukaryotes. This provid es the potential to apply genetic and molecular approaches to study ge ne products and mechanisms involved in this type of protein distributi on. The selection strategy also offers a new approach for identifying gene products involved in the distribution of proteins to their subcel lular destinations.