Protein stability regulates the expression of cytochrome c during the developmental cycle of Trypanosoma brucei

The expression of cytochrome c is developmentally regulated during the life cycle of Trypanosoma brucei. The level of regulation appears to be post-transcriptional since cytochrome c mRNA is present in all life stages of the parasite. We have used RNA from each life stage to prime in vitro translation systems and found that the cytochrome c mRNAs are equally translatable. Continuous labeling experiments conducted in vivo indicate that cytochrome c is synthesized at similar rates in both bloodstream and procyclic trypanosomes. Western blots, however, confirm that steady-state levels of cytochrome c are severely depressed in bloodstream forms. In a series of pulse/chase experiments we demonstrate that the half-life of cytochrome c is approximately 1 h in the bloodstream form and no detectable turnover occurred in the procyclic form. We conclude that a major step in the developmental regulation of cytochrome c expression in T. brucei occurs post-translationally due to rapid turnover of the protein in the bloodstream trypanosomes.