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Yeast mitochondrial NAD(+)-dependent isocitrate dehydrogenase is an RNA-binding protein
S D Elzinga1, A L Bednarz, K van Oosterum
1Department of Molecular Cell-Biology, University of Amsterdam, The Netherlands.
Abstract:
We have previously described the characterisation of an abundant mitochondrial protein (p40) that binds specifically to 5'-untranslated leaders of mitochondrial mRNAs in yeast. p40 consists of two polypeptides with M(r) of 40 and 39 kDa. Limited sequence analysis of p40 identifies it as the Krebs cycle enzyme NAD(+)-dependent isocitrate dehydrogenase (Idh). Both enzyme and RNA-binding activities are specifically lost in cells containing disruptions in either IDH1 or IDH2, the nuclear genes encoding the two subunits of the enzyme, thus conclusively identifying p40 as Idh and showing that both activities are dependent on the simultaneous presence of both subunits. Although we still must ascertain whether and how either function of Idh is regulated and whether the two functions are compatible or mutually exclusive, this combination of dehydrogenase activity and RNA-binding in a single protein may be part of a general regulatory circuit linking the need for mitochondrial function to mitochondrial biogenesis.
Insights
A yeast mitochondrial protein, p40, is identified as NAD(+)-dependent isocitrate dehydrogenase (Idh). This Idh enzyme also binds mitochondrial mRNA leaders, suggesting a link between cellular energy needs and mitochondrial gene expression.
Area of Science:
- Mitochondrial biology
- Molecular genetics
- Biochemistry
Background:
- An abundant mitochondrial protein (p40) in yeast was previously characterized for its specific binding to 5'-untranslated leaders of mitochondrial mRNAs.
- p40 comprises two polypeptides with molecular masses of 40 and 39 kDa.
Purpose of the Study:
- To identify the molecular identity of the p40 protein.
- To determine the functional relationship between the identified protein and its RNA-binding activity.
Main Methods:
- Limited protein sequence analysis was performed on purified p40.
- Genetic analysis involved studying yeast cells with disruptions in the nuclear genes IDH1 and IDH2.
Main Results:
- Sequence analysis identified p40 as NAD(+)-dependent isocitrate dehydrogenase (Idh).
- Both Idh enzyme activity and RNA-binding activity were lost in yeast strains lacking IDH1 or IDH2.
- These findings demonstrate that both functions depend on the presence of both Idh subunits.
Conclusions:
- The mitochondrial protein p40 is conclusively identified as Idh, a key Krebs cycle enzyme.
- Idh possesses both dehydrogenase and mitochondrial mRNA binding activities.
- This dual function suggests a regulatory mechanism connecting mitochondrial energy production with mitochondrial biogenesis.