Intramitochondrial Functions Regulate Nonmitochondrial Citrate Synthase (CIT2) Expression in Saccharomyces cerevisiae

Abstract

We have examined the effects of perturbation of mitochondrial function on expression of two nuclear genes encoding the mitochondrial and peroxisomal forms of citrate synthase in Saccharomyces cerevisiae, CIT1 and CIT2. CIT2 expression was as much as 30-fold higher in [rho⁰] petites, than in isochromosomal [rho⁺] cells, whereas CITI expression was slightly down regulated in [rho⁰] cells. CIT2 expression was also increased in [rho⁺] cells by inhibition of respiration with antimycin A or in [rho⁺] cells containing a disruption of the CITI gene. These effects were additive, and together they approached the level of CIT2 expression seen in [rho⁰] cells. Experiments using heterologous gene fusions showed that all of the effects leading to increased expression of CIT2 were transcriptionally controlled through 5′-flanking CIT2 DNA sequences. Analysis of [rho⁺] and [rho⁰] cells containing disruptions of CITI and CIT2, singly and in combination, showed that the peroxisomal citrate synthase could partially spare the mitochondrial isoform for growth yield in [rho⁺] but not in [rho⁰] cells. These studies suggest a physiological role for increased expression of CIT2 in cells with altered mitochondrial function. They also provide additional evidence for a retrograde path of communication from mitochondria to the nucleus in yeast cells.