Adenine nucleotide transport via Sal1 carrier compensates for the essential function of the mitochondrial ADP/ATP carrier.

The mitochondrial ADP/ATP carrier (Aac2p) of Saccharomyces cerevisiae links two biochemical pathways, glycolysis in the cytosol and oxidative phosphorylation in the mitochondria, by exchanging their common substrates and products across the inner mitochondrial membrane. Recently, the product of the SAL1 gene, which is essential in cells lacking Aac2p, has been implicated in a similar communication. However, the mechanism by which Sal1p rescues the growth of Deltaaac2 mutants is not clear and it was proposed that both Sal1p and Aac2p share a common vital function other than ADP/ATP exchange. Here, the impact of SAL1 deletion on mitochondrial reactions involving either synthesis or hydrolysis of ATP was investigated. We show that adenine nucleotide transport activity related to Sal1p can be demonstrated in isolated mitochondria as well as in intact cells under conditions when Aac2-mediated exchange is not functional. Our results indicate that the vital role of both Sal1p and Aac2p is to maintain the essential intramitochondrial ATP pool owing to their ability to transport adenine nucleotides.