Translation of mitochondrial RNA from yeast cytoplasmic petite mutants in an E. coli cell-free system

Translation of polyuridylic acid in lysed mitochondria

After osmotic shock with 50 mM Tricine buffer (pH 7.9), isolated mitochondria from D. Melanogaster embryos are treated with a low concentration of Triton X-100 (25 micrograms/mg of protein). The lysed mitochondria are still capable of RNA and protein synthesis. While incorporation of labeled precursor is often higher in lysed than in intact mitochondria, neosynthesized proteins exhibit similar electrophoretic patterns. Studies of labeled precursor incorporation in the presence of various effectors indicate a better accessibility to the translation machinery in lysed mitochondria than in intact mitochondria. Such a system has proven capable of translating an exogenous synthetic mRNA, i.e., poly (U).

On the cell-free system of protein synthesis from mammalian mitochondria

Some properties of a submitochondrial cell-free system for protein synthesis are described. The system was prepared from rat liver mitochondria lysed with Triton X-100, and the lysate was characterized by a linear rate of [14C]amino acid incorporation for 15-20 min with subsequent decline in activity. The incorporation reaction was inhibited by chloramphenicol and was insensitive to cycloheximide. Poly(U) addition stimulated [14CA1phenylalanine incorporation by the preincubated submitochondrial system. Upon the addition of 7.5S mRNA that was isolated from mitochondria the major translation product was identified as a hydrophobic poly-peptide which in some properties (solubility in chloroform-methanol mixture) was similar to one of polypeptides synthesized by the sub-mitochondrial system on endogeneous mRNAs.

Variant forms of mitochondrial translation products in yeast: evidence for location of determinants on mitochondrial DNA

Products of mitochondrial protein synthesis in yeast have been labeled in vivo with 35SO42-. More than 20 polypeptide species fulfilling the criteria of mitochondrial translation products have been detected by analysis on sodium dodecyl sulfate-exponential polyacrylamide slab gels. A comparison of mitochondrial translation products in two wild-type strains has revealed variant forms of some polypeptide species which show genetic behavior consistent with the location of their structural genes on mtDNA. Our results demonstrate the feasibility of performing genetic analysis on putative gene products of mtDNA in wild-type yeast by direct examination of the segregation and recombination behavior of specific polypeptide species.