Abstract
Abstract Effects of two antibiotics, chloramphenicol and cycloheximide, on the synthesis of mitochondrial and cytoplasmic ribosomes in Tetrahymena were studied. The results presented here show that mitochondrial ribosome synthesis was not completely inhibited by chloramphenicol (0.5 mm), but was abolished by cycloheximide (1 mm). Acrylamide gel electrophoresis analysis revealed that mitochondrial ribosomal proteins in a range of molecular weights from 13,000 to 25,000 were found particularly susceptible to chloramphenicol inhibition. Cytoplasmic ribosomal proteins did not appear to be differentially inhibited by chloramphenicol. The inhibition of mitochondrial ribosome synthesis in the presence of cycloheximide did not result from the loss of mitochondrial protein synthesis capacity as evidenced by in vitro [14C]leucine incorporation capacity of mitochondria isolated from whole cells treated with cycloheximide. However, cycloheximide greatly reduces the capacity to incorporate [3H]uridine into mitochondrial ribosomes as RNaseresistant radioactivity. These results suggest that some mitochondrial ribosomal proteins are synthesized in mitochondria and others by cytoplasmic ribosomes. The synthesis of those proteins that are produced by the mitochondrial ribosomes appears to be under the control of cytoplasmic protein synthesis. However, mitochondrial ribosome assembly can take place in the absence of cytoplasmic protein synthesis.
Highlights
Effects of two antibiotics, chloramphenicol and cycloheximide, on the synthesis of mitochondrlal and cytoplasmic ribosomes in Tefrohymena were studied
Comparison of the radioactivity profile of gel slices from chloramphenicol-treated mitochondrial ribosomes reveals that synthesis of mitochondrial ribosomal protein in the range from 13,000 to 25,000 molecular weight appears completely suppressed in relation to those of high molecular weight (Fig. 6)
Since no incorporation of amino acids was detected in cycloheximidetreated mitochondrial ribosomes, proteins regulated by cytoplasmic protein synthesis may control the synthesis of mitochondrial ribosomal protein
Summary
Chloramphenicol and cycloheximide, on the synthesis of mitochondrlal and cytoplasmic ribosomes in Tefrohymena were studied. The inhibition of mitochondrial ribosome synthesis in the presence of cycloheximide did not result from the loss of mitochondrial protein synthesis capacity as evidenced by in vitro Mitochondrial ribosome assembly can take place in the absence of cytoplasmic protein synthesis. Fractions 20 to 32 were collected after sucrose gradient centrifrl g&ion (see Fig. 2), pooled, a.nd assayed for protein and acitl-ill soluble radioactivity. Sucrose gradient centrifugation analysis of cytoplasmic and mitochondrial extracts revealed that ribosomal regions from both sources receive significant radioactivity (Fig. 2). In these experiments the culture was treated with antibiotics for 15 min
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