A NOVEL PHOSPHOPANTETHEINE-PROTEIN TRANSFERASE ACTIVATING YEAST MITOCHONDRIAL ACYL CARRIER PROTEIN

In Saccharomyces cerevisiae, the low molecular weight acyl carrier pro tein (ACP) of mitochondrial type ZI fatty acid synthase (FAS) and the cytoplasmic type I FAS multienzyme contain 4'-phosphopantetheine as a prosthetic group. Sequence alignment studies with the recently isolate d phosphopantetheine:protein transferase (PPTase), Ppt1p, from Breviba cterium ammoniagenes revealed the yeast open reading frame, YPL148C, a s a potential PPTase gene (25% identical and 43% conserved amino acids ). In accordance with this similarity, pantetheinylation of mitochondr ial ACP was lost upon disruption of YPL148C. In contrast, biosynthesis of cytoplasmic holo-FAS remained unaffected by this mutation. Accordi ng to these characteristics, the newly identified gene was designated as PPT2. Similar to ACP null mutants, cellular lipoic acid synthesis a nd, hence, respiration were abolished in PPT2 deletants. ACP pantethei nylation, Lipoic acid synthesis, and respiratory competence were resto red upon transformation of PPT2 mutants with cloned PPT2 DNA, In vitro , holo-ACP synthesis was achieved by incubating apo-ACP with coenzyme A in the presence of purified Ppt2p. The homologous yeast enzyme could be replaced, in this assay, by the ACP synthase (EC 2.7.8.7) of Esche richia coli but not by the type I FAS-specific PPTase of B. ammoniagen es, Ppt1p. These results conform with the inability of Ppt2p to activa te the cytoplasmic type I FAS complex of yeast.