Isolation and characterization of mitochondrial nucleoids from the yeast Pichia jadinii

Mitochondrial (mt) nucleoids were isolated with a high degree of purity from the yeast Pichia jadinii, in which the mitochondrial DNA (mtDNA) is linear. Field-inversion gel electrophoresis (FIGE) revealed that significant amounts of mtDNA could be isolated intact, as linear molecules of 41 kbp, from the isolated mt-nucleoids. Fifteen different proteins were detected in the mt-nucleoid fraction and, eight of these proteins bound to DNA. The patterns of mt-nucleoid proteins and of the DNA-binding proteins after gel electrophoresis in the presence of SDS were somewhat different from those of such proteins from Saccharomyces cerevisiae. The corresponding proteins isolated from the mt-nucleoids of four other species of yeast in the genera Pichia and Williopsis also differed from one another in terms of electrophoretic mobility in the presence of SDS. In immunoblotting experiments, antibodies that had been raised against the 67-kDa protein of mt-nucleoids from S.cerevisiae and the YMN-1 monoclonal antibody that is specific for a 48-kDa protein in the mt-nucleoids from S. cerevisiae did not recognize any proteins in the mt-nucleoids from Pichia jadinii and four other species of yeast. The results suggest the considerable diversity of the proteins in the mt-nucleoids of yeasts.