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DNA from the cloned yeast iso-1-cytochrome c, cycl, gene was used in a hybridization assay to measure levels and rates of synthesis of cycl RNA. Derepressed cells synthesized cycl RNA at 6 times the rate of that of glucose-repressed cells. Upon glucose addition to a derepressed culture, the transcription of the cycl gene was repressed within 2.5 min. The half-life of hybridizable cycl RNA was determined to be 12-13.5 min under repressed and derepressed conditions and during repression. The results demonstrate that the expression of the cycl gene is subject to transcriptional regulation.

The effects of the mitochondrial protein synthesis inhibitor chloramphenicol and the mitochondrial F0 adenosine triphosphatase inhibitor oligomycin on the synthesis of nucleus-encoded cytochrome c protein were studied. Both inhibitors stimulated cytochrome c protein synthesis in the derepressed state (growth in media containing 2% raffinose) but had no effect on the synthesis of the cytochrome c protein in the repressed state (growth in media containing 5% glucose). Oligomycin uncoupled the synthesis of the apoprotein from its processing into the hemoprotein. Neither antibiotic had a significant effect on the rate of glucose repression of cytochrome protein synthesis. The kinetics of cytochrome c derepression and the effects of these two antibiotics on these kinetics were also studied. Cells were derepressed by transfer from glucose- to faffinose-containing media, and the rate of cytochrome c synthesis increased from the repressed to the derepressed level during the second hour of derepression. Chloramphenicol delayed this derepression, but after 5 h the rate of cytochrome c protein synthesis increased to twice the rate of synthesis in uninhibited cells. On the other hand, oligomycin inhibited derepression of cytochrome c. These results are discussed with respect to the effects of mitochondrial function in the derepressed and repressed states and during the processes of repression and derepression of cytochrome c.