CYTOPLASMIC AND MITOCHONDRIAL FORMS OF YEAST ADENYLATE KINASE-2 ARE N-ACETYLATED

Yeast major adenylate kinase (Aky2p), encoded by a single gene, occurs in two subcellular compartments, mitochondria and cytoplasm. Only 6-8 % of the protein which has no cleavable presequence is imported into t he organelle (Bandlow et al. (1988) fur. J. Biochem. 178, 451-457). In the wild type two AKY2-derived signals (a major and a minor one) were detected by a monospecific antibody after two-dimensional gel electro phoresis and Western blotting. The signals reflected identical electro phoretic mobilities and were absent from an AKY2-disrupted strain sugg esting that they were due to differently modified forms of Aky2p. Two similar signals were found in a mutant defective in protein N-acetylat ion, however, the pI values of both spots were shifted towards alkalin e pH by one charge. This indicated that both forms of Aky2p were N-ace tylated in the wild type and that their charge difference was not caus ed by incomplete N-acetylation. This observation furthermore suggested that, in the wild type, two different modifications exist one of whic h is N-acetylation. The second modification remains unidentified. We a nalysed the influence of protein N-acetylation on mitochondrial import . Both versions of Aky2p occurred in the cytoplasm and in mitochondria . Their proportion was unchanged in the N-acetylation mutant showing t hat neither modification affected the efficiency of import of adenylat e kinase into mitochondria. It is discussed that N-acetylation occurs during or immediately after translation in the cytoplasm so that impor t of adenylate kinase may ensue co-translationally.