Preparation of a Monoclonal Antibody Specific for a 48-kDa Protein from Mitochondrial Nucleoids of the Yeast, Saccharomyces cerevisiae

Monoclonal antibodies (mAbs) were raised against yeast mitochondrialnucleoids (mtnucleoids). In an analysis by a combination ofimmunofluorescence microscopy and staining with 4',6-diamidino-2-phenylindole(DAPI), one of them, designated YMN-1, distinctly stained mtnucleoids,which were visible as dots, in spheroplasts and in isolatedmitochondria. However, staining of isolated mt-nucleoids wasrather weak. YMN-1 mAb recognized a 48-kDa protein in immunoblotsof both mitochondrial and mt-nucleoid proteins. The 48-kDa proteinwas a minor component of mt-nucleoid proteins and was separatedfrom extract of both mitochondria and mt-nucleoids by immunoamnitychromatography. The affinity-purified 48-kDa protein reassociatedwith mt-nucleoids when mixed with isolated mt-nucleoids, asmonitored by immunofluorescence microscopy. The results suggestthat a large amount of 48-kDa protein is associated with mt-nucleoidsin vivo, and that lysis of mitochondria by the treatment withdetergent releases a considerable amount of this protein frommt-nucleoids during the isolation of mt-nucleoids. (Received June 25, 1992; Accepted November 16, 1992)