UTP-Dependent and -Independent Pathways of mRNA Turnover in Trypanosoma brucei Mitochondria

Abstract

Although primary transcripts are polycistronic in the mitochondria of Trypanosoma brucei, steady-state levels of mature, monocistronic RNAs change throughout the parasitic life cycle. This indicates that steady-state RNA abundance is controlled by posttranscriptional mechanisms involving differential RNA stability. In this study, in organello pulse-chase labeling experiments were used to analyze the stability of different T. brucei mitochondrial RNA populations. In this system, total RNA and rRNA are stable for many hours. In contrast, mRNAs can be degraded by two biochemically distinct turnover pathways. The first pathway results in the rapid degradation of mRNA (half-life [t _1/2] of 11 to 18 min) and is dependent upon the presence of an mRNA poly(A) tail. Remarkably, this pathway also requires the addition of UTP and therefore is termed UTP dependent. The second pathway results in slow turnover of mitochondrial mRNA (t _1/2 of ∼3 h) and is not dependent upon the presence of an mRNA poly(A) tail or the addition of exogenous UTP. In summary, these results demonstrate the presence of a novel, UTP-dependent degradation pathway for T. bruceimitochondrial mRNAs and reveal an unprecedented role for both UTP and mRNA polyadenylation in T. brucei mitochondrial gene expression.

ACKNOWLEDGMENTS

We thank V. James Hernandez for helpful discussions throughout the course of this work. In addition, we thank Tom Melendy, V. J. Hernandez, and members of the Read lab for critical reading and discussion of the manuscript.

This work was supported in part by NIH grant GM53502 to L.K.R., who is also a recipient of the Burroughs Wellcome Fund New Investigator Award in Molecular Parasitology.