IRC3 regulates mitochondrial translation in response to metabolic cues in Saccharomyces cerevisiae

Mitochondrial oxidative phosphorylation (OXPHOS) enzymes are made up of dual genetic origin. Mechanism regulating expression of nuclear encoded OXPHOS subunits in response to metabolic cues (glucose vs. glycerol), is significantly understood while regulation of mitochondrially encoded OXPHOS subunits is poorly defined. Here, we show that IRC3 a DEAD/H box helicase, previously implicated in mitochondrial DNA maintenance, is central to integrating metabolic cues with mitochondrial translation. Irc3 associates with mitochondrial small ribosomal subunit in cells consistent with its role in regulating translation elongation based on Arg8m reporter system. Glucose grown{Delta} irc3{rho}+ and irc3 temperature sensitive cells at 37C have reduced translation rates from majority of mRNAs. In contrast, when galactose was the carbon source, reduction in mitochondrial translation was observed predominantly from Cox1 mRNA in{Delta} irc3{rho}+ but no defect was observed in irc3 temperature sensitive cells, at 37C. In support, of a model whereby IRC3 responds to metabolic cues, suppressors of {Delta}irc3 isolated for restoration of growth on glycerol media restore mitochondrial translation differentially in presence of glucose vs. glycerol.