In vitro reconstruction of the mitochondrial translation system of yeast

We have isolated the translation system from yeast mitochondria and have reconstructed it in vitro. This submitochrondrial system, composed of mitochondrial ribosomes, tRNA, pH 5 fraction and mRNA,is maximally active at 10 mM Mg²⁺ and 100 mM KCl or NH₄Cl. NH₄⁺ is more stimulatory than K⁺. Added Escherichia coli tRNA gives less than half the activity obtained with added mitochondrial tRNA. Activity is enhanced with protease inhibitors but not with Ca²⁺, spermine, or spermidine. In contrast to heterologous translation systems, the present system produces products with molecular weights similar to those of products synthesized by yeast mitochondria in vivo and by intact yeast mitochondria in vitro. The results support the idea that the unique coding features of the mitochondiral genome require a unique translation system for accurate translation of mitochondrial mRNAs.