Incorporation in vivo of “C-Labelled Amino Acids into the Proteins of Mitochondria1 Ribosomes from Neurospora crassa Sensitive to Cycloheximide and Insensitive to Chloramphenicol

Radioactive amino acids were incorporated in vivo into Neurospora crassa cells, and the mitochondrial ribosomes were isolated. The incorporat,ion of radioactivity into the proteins of these ribosomes was inhibited by cycloheximide, but not by chloramphenicol. It is therefore concluded that these proteins are synthesized on the cycloheximide sensitive and chloramphenicol insensitive cytoplasmic ribosomes. Biogenesis of mitochondria involves the coopera-tion of two systems of protein synthesis, one extra-mitochondrial (extrinsic) and one mitochondrial (intrinsic). In order to investigate the contribution of one system, the other has to be separated. In the preceding paper we reported on the intrinsic in-corporation of amino acids by mitochondrial ribo-somes in vitro in isolated mitochondria [l]. In the present experiments, separation of the mitochondrial and extramitochondrial system was achieved in viv