Structural protein prepared from mitochondria of wild-type baker's yeast contains several components which are separable by electrophoresis on polyacrylamide gels. One of these components is absent from structural protein preparations obtained from a cytoplasmic "petite" mutant.Rabbit antisera against the structural protein of yeast mitochondria are capable of agglutinating yeast mitochondria and human erythrocytes coated with yeast mitochondrial structural protein. The agglutination of coated erythrocytes can be inhibited by absorption of antisera with structural protein. With the help of this sensitive haemagglutination-inhibition technique the antigenic properties of structural protein from mitochondria of the wild-type yeast and the "petite" mutant were compared. It was found that at least one of the antigenic determinants present in the mitochondrial structural protein preparations from wild-type yeast is lacking in those obtained from the mutant.Saccharomyces cerevisiae easily undergoes nonchromosomal mutations which result in loss of respiratory capacity. The mutants derive the energy required for growth and reproduction exclusively from fermentation and therefore form small colonies on solid media poor in glucose. The mitochondria of the "petite" mutants differ from normal yeast mitochondria both morphologically and biochemically [1,2]. The respiratory block has been accounted for by a total absence from the mitochondria of cytochrome oxidase and a complete or near complete deficiency in cytochromes b and c1 [3]. Mitochondria1ATPase associated with the "petite" yeast mitochondria is cold-labile and oligomycin-insensitive [4], whereas the same enzyme in wild-type mitochondria is stable to cold and sensitive to oligomycin 151.It is likely that the extrachromosomal genetical factor(s) involved in the petite mutation are located in the mitochondria themselves. Isolated yeast mitochondria, like mitochondria of other organisms, contain a DNA species which differs from chromosomal DNA with respect to base composition, melting behaviour and buoyant density [S-81. Studies on isolated mitochondria have indicated that the endogenous DNA has an important role in mitochondrial RNA and protein synthesis [9,10]. As first shown for Unusual Abbreviations. SP, structural protein of yeast mitochondria ; wSP, structural protein from mitochondria of wild-type yeast; pSP, structural protein from mitochondria of a cytoplasmic ("petite colonie") mutant.Enzyme. ATPase or ATP phosphohydrolase (EC 3.6.1.3).
2.3.isolated rat-liver mitochondria, radioactive aminoacids are incorporated predominantly into an insoluble protein fraction [l I, 121 which resembles mitochondrial "structural protein" [13]. I n contrast, the components of the respiratory chain are only insignificantly labelled. These results suggest that structural protein may be a main product of the mitochondrial genetic system. The "petite" mutation has been shown not to deprive the yeast mitochondria of all of their endogenous DNA but to result in a marked change of its ...