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Substrates for yeast mitochondrial cAMP-dependent protein kinase activity
1Department of Microbiology and Immunology, Medical College of Pennsylvania/Hahnemann University, Philadelphia, USA.
Biochemical and Biophysical Research Communications
|September 5, 1995
Summary
Cellular cAMP levels regulate mitochondrial gene transcription via cAMP-dependent protein kinase (cAPK) in Saccharomyces cerevisiae. This study identifies eight mitochondrial proteins phosphorylated by mt cAPK, revealing insights into gene regulation.
Area of Science:
- Mitochondrial biology
- Gene expression regulation
- Biochemistry
Background:
- Mitochondrial gene transcription in Saccharomyces cerevisiae is influenced by cellular cyclic adenosine monophosphate (cAMP) levels.
- This regulation is mediated by cAMP-dependent protein kinase (cAPK) activity.
Purpose of the Study:
- To identify specific protein substrates for mitochondrial cAMP-dependent protein kinase (mt cAPK) using in vitro assays.
- To investigate the role of Mtflp, the mitochondrial RNA polymerase specificity factor, in mt cAPK-mediated phosphorylation.
- To determine the contribution of individual catalytic subunits of mt cAPK to the phosphorylation of identified substrates.
Main Methods:
- In vitro protein kinase assays using intact mitochondria isolated from respiring Saccharomyces cerevisiae cells.
- Analysis of protein phosphorylation patterns in wild-type and mtf1 mutant strains.
- Characterization of substrate phosphorylation using double mutants for TPK1, TPK2, and TPK3 genes encoding catalytic subunits of mt cAPK.
Main Results:
- At least eight distinct mitochondrial proteins, with molecular masses ranging from 96,000 to 9,500 M(r), are phosphorylated in a cAMP-dependent manner.
- The mitochondrial RNA polymerase specificity factor, Mtflp, was not found to be a target protein requiring phosphorylation for its activity.
- Phosphorylation of the eight identified mt substrate proteins is not equivalent across the individual catalytic subunits (encoded by TPK1, TPK2, and TPK3) of the mt cAPK.
Conclusions:
- Mitochondrial gene transcription is subject to regulation by cellular cAMP levels through mt cAPK activity.
- Specific mitochondrial proteins are phosphorylated by mt cAPK, indicating a role in post-translational modification of mitochondrial components.
- Mtflp's function is independent of direct phosphorylation by mt cAPK, and the catalytic subunits of mt cAPK exhibit differential substrate specificities.