Abstract
The biosynthesis of yeast mitochondrial Phe-tRNA synthetase is studied in vivo. Antibodies against the enzyme are raised in rabbits. They precipitate two proteins in the post-ribosomal supernatant of the yeast cell homogenate. Immunoprecipitate analysis on SDS - gel electrophoresis shows that the two types of mitochondrial enzyme subunits with molecular weights of 57,000 and 72,000, respectively, are cytoplasmically synthesized as larger, individual precursors. Terminal extensions of the precursors prevent enzyme activity. Mitochondrial membranes linked protease(s) play(s) an active role in maturation.