Cytological studies on mitochondria-induced cytoplasmic transformation in yeasts

Publisher Website
Google Scholar
Abstract
In Saccharomyces cerevisiae, protoplasts from respiratory-deficient (rho−) cytoplasmic mutant cells were transformed into respiratory-sufficient (rho+) cells by incubation with mitochondria prepared from rho+ cells in the presence of polyethylene glycol and CaCl2. Mitochondria prepared from different species, Hansenula wingei and Schizosaccharomyces pombe, also caused the transformation of S. cerevisiae rho− protoplasts into the rho+ cells as previously reported (14) The obtained transformants were confirmed to contain one nucleus and several mitochondrial DNAs by fluorescent staining of DNA. The transformants clearly restored cytochromes a and b while untransformed recipient cells lacked the cytochromes. In order to know the mechanism of the transformation, physiological measurement of endocytotic activity of protoplasts and cytological examination of mitochondria-protoplast aggregates under the transforming condition were performed. Protoplasts had significant endocytotic activity under this condition. On the other hand, fluorescence and electron microscopic observations indicated that mitochondria forming aggregates with protoplasts were subsequently integrated into recipient protoplasts through fusion rather than endocytosis. However, the possibility of endocytosis could not be completely excluded when the low frequency of the transformation (about 10−6 to 10−7) was taken into account. This is discussed in this paper. A new convenient method for measuring endocytosis is also presented.