Synthesis of mitochondrial proteins in an Escherichia coli cell-free system directed by yeast mitochondrial DNA.

The optimum conditions for transcription in vitro of yeast mtDNA into biologically relevant RNA by Escherichia coli RNA polymerase holoenzyme and yeast mitochondrial RNA polymerase was found to critically depend on salt concentration. RNA was transcribed (at 0.25 M KCl concentration) from high-molecular-weight mtDNA which was then translated in an E. coli (S-30) cell-free protein synthesising system. Efficient translation of mitochondrial RNA was achieved using conditions which had also been determined to be optimal in other systems. Identification of the polypeptides produced in the translation system was made using antiserum raised against mitochondrial membranes. Electrophoresis of the completely dissociated antigen-antibody complexes using dodecylsulphate-polyacrylamide gels revealed that the system in vitro produced polypeptides of similar molecular weight to those synthesised in vivo by cycloheximide-inhibited whole cells.