SUBCELLULAR RELOCALIZATION OF A LONG-CHAIN FATTY-ACID COA LIGASE BY ASUPPRESSOR MUTATION ALLEVIATES A RESPIRATION DEFICIENCY IN SACCHAROMYCES-CEREVISIAE

We have isolated an extragenic suppressor, FAM1-1, which is able to re store respiratory growth to a deletion of the CEM1 gene (mitochondrial beta-keto-acyl synthase), The sequence of the suppressor strongly sug gests that it encodes a long-chain fatty acid CoA ligase (fatty-acyl-C oA synthetase), We have also cloned and sequenced the wild-type FAM1 g ene, which is devoid of suppressor activity, The comparison of the two sequences shows that the suppressor mutation is an A-->T transversion , which creates a new initiation codon and adds 18 amino acids to the N-terminus of the protein, This extension has all the characteristics of a mitochondrial targeting sequence, whilst the N-terminus of the wi ld-type protein has none of these characteristics. In vitro mitochondr ial import experiments show that the N-terminal half of the suppressor protein, but not of the wild-type, is transported into mitochondria. Thus, we hypothesize that the suppressor acts by changing the subcellu lar localization of the protein and relocating at least some of the en zyme from the cytosol to the mitochondria. These results support the h ypothesis that some form of fatty acid synthesis, specific for the mit ochondria, is essential for the function of the organelle.