Intersection of RNA Processing and the Type II Fatty Acid Synthesis Pathway in Yeast Mitochondria

Abstract

Distinct metabolic pathways can intersect in ways that allow hierarchical or reciprocal regulation. In a screen of respiration-deficient Saccharomyces cerevisiae gene deletion strains for defects in mitochondrial RNA processing, we found that lack of any enzyme in the mitochondrial fatty acid type II biosynthetic pathway (FAS II) led to inefficient 5′ processing of mitochondrial precursor tRNAs by RNase P. In particular, the precursor containing both RNase P RNA (RPM1) and tRNA^Pro accumulated dramatically. Subsequent Pet127-driven 5′ processing of RPM1 was blocked. The FAS II pathway defects resulted in the loss of lipoic acid attachment to subunits of three key mitochondrial enzymes, which suggests that the octanoic acid produced by the pathway is the sole precursor for lipoic acid synthesis and attachment. The protein component of yeast mitochondrial RNase P, Rpm2, is not modified by lipoic acid in the wild-type strain, and it is imported in FAS II mutant strains. Thus, a product of the FAS II pathway is required for RNase P RNA maturation, which positively affects RNase P activity. In addition, a product is required for lipoic acid production, which is needed for the activity of pyruvate dehydrogenase, which feeds acetyl-coenzyme A into the FAS II pathway. These two positive feedback cycles may provide switch-like control of mitochondrial gene expression in response to the metabolic state of the cell.

ACKNOWLEDGMENTS

We dedicate this paper to Stuart Brody, who discovered the acyl carrier protein in yeast (6) and launched the study of mitochondrial fatty acid biosynthesis.

We thank Telsa Mittelemeier and John Little for critical reading of the manuscript, Zsuzsanna Fekete for helpful discussions and suggestions, and Mike Rice and Tim Ellis for help in the laboratory. We also thank Lee McAlister-Henn for the generous gift of anti-IDH antisera.

M.S.S. was supported by a fellowship from the National Science Foundation Integrative Graduate Education and Research Traineeship Program in Evolutionary, Functional and Computational Genomics at the University of Arizona and by the National Institutes of Health Graduate Training in Biochemistry and Molecular Biology grant T3208659. This work was supported by National Institutes of Health grant GM34893 to C.L.D.