Messenger RNA metabolism in mammalian mitochondria. III. Messenger ribonucleic acid metabolism in mammalian mitochondria. Isolation and characterization of polyribosomes from Ehrlich ascites mitochondria

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Abstract
The Mg2+ precipitation procedure of R. D. Palmiter (1974) was used for preparative scale isolation of polysomes from Ehrlich ascites mitochondria. Digitonin-washed mitochondria used for isolating the polysomes contain no detectable NADPH-cytochrome c reductase and over 200-fold reduced hexokinase activity. The mitochondrial polysomes exhibit a heterogeneous sedimentation and appear to contain highly aggregated particles ranging over hexamers. These polysomes are sensitive to RNase, (ethylenedinitrilo) tetraacetic acid and puromycin. Mitochondrial polysomes are active in protein synthesis when supplied with supernatant enzymes from the homologous mitochondrial source or from Escherichia coli. Cytoplasmic enzymes, however, appear to be completely inactive. Protein synthesis by mitochondrial polysomes is sensitive to chloramphenicol and resistant to cycloheximide and emetine. The procedure yields particles containing intact rRNAs. The extent of cytoplasmic RNA contaminating the total mitochondrial RNA or mitochondrial polysomal RNA was estimated to be negligible.