Transactivation by Rtg1p, a basic helix-loop-helix protein that functions in communication between mitochondria and the nucleus in yeast.
Rtg1p is a basic helix-loop-helix transcription factor in the yeast Saccharomyces cerevisiae that is required for basal and regulated expression of CIT2, the gene encoding a peroxisomal isoform of citrate synthase. In respiratory incompetent rho degree petite cells, CIT2 transcription is elevated as much as 30-fold compared with respiratory competent rho + cells. Here we provide evidence that Rtg1p interacts directly with a CIT2 upstream activation site (UASr) and that the rho degree/rho + regulation is not due to a change in the levels of Rtg1p. A fusion protein consisting of the DNA binding domain of Gal4p fused to the NH2 terminus of the full-length wild-type Rtg1p was able to transactivate an integrated LacZ reporter under control of the Gal4p-responsive GAL1 UASG in a rho degree/rho(+)-dependent manner. Other Gal4p fusions to deletions or mutations of Rtg1p indicate that the helix-loop-helix domain is essential for transactivation. Regulated expression of CIT2 also requires the RTG2 gene product. The Gal4-Rtg1p fusion was unable to transactivate the LacZ reporter gene in a strain deleted for RTG2, suggesting that the RTG2 product does not act independently of Rtg1p in the rho degree/rho + transcriptional response.
D000483:Alleles; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D002467:Cell Nucleus / Q000502:physiology; D002950:Citrate (si)-Synthase / Q000235:genetics; D004247:DNA / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology*; D017930:Genes, Reporter; D018257:Helix-Loop-Helix Motifs; D047908:Intracellular Signaling Peptides and Proteins; D008928:Mitochondria / Q000502:physiology; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators / Q000502:physiology*; D014157:Transcription Factors
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; C079378:RTG1 protein, S cerevisiae; C079379:RTG2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D004247:DNA; D002950:Citrate (si)-Synthase