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Comparison of populations of mRNA coding fumarase in rat brain and liver
Abstract:
The populations of mRNA encoding mitochondrial and cytosolic fumarases in the poly A+ RNA fractions purified from polysomes of rat brain and liver were examined. When the in vitro translation products programmed by the poly A+ RNA fraction obtained from rat brain were purified by immunoprecipitation with anti-fumarase antibody and analyzed by SDS polyacrylamide gel electrophoresis and fluorography, only one polypeptide of 50 KD was detected as a precursor of fumarase. In contrast, by the same method, two polypeptides of 50 KD and 45 KD, which is the same size as mature fumarase, were detected as precursors of rat liver fumarase. These results suggest that rat brain polysomes contain only one population of mRNA coding a 50 KD precursor of mitochondrial fumarase with little or no mRNA of the cytosolic fumarase, whereas rat liver polysomes contain two types of mRNA for mitochondrial and cytosolic fumarases, respectively. These findings are consistent with the fact that the brain is the only organ in rats known not to contain cytosolic fumarase.
Insights
Rat brain mRNA primarily codes for mitochondrial fumarase precursor, while rat liver mRNA codes for both mitochondrial and cytosolic fumarase precursors. This reflects tissue-specific expression of fumarase enzymes.
Area of Science:
- Biochemistry
- Molecular Biology
- Neuroscience
Background:
- Fumarase is a key enzyme in the Krebs cycle, existing in both mitochondrial and cytosolic forms.
- Tissue-specific expression of fumarase isoforms suggests differential gene regulation.
Purpose of the Study:
- To investigate the populations of mRNA encoding mitochondrial and cytosolic fumarases in rat brain and liver.
- To understand the molecular basis for the absence of cytosolic fumarase in the rat brain.
Main Methods:
- Isolation of polyadenylated RNA (poly A+ RNA) from rat brain and liver polysomes.
- In vitro translation of RNA fractions.
- Immunoprecipitation using anti-fumarase antibody.
- Analysis of translation products by SDS-polyacrylamide gel electrophoresis and fluorography.
Main Results:
- Rat brain mRNA produced a single 50 KD polypeptide precursor for fumarase.
- Rat liver mRNA produced two polypeptide precursors: 50 KD (mitochondrial) and 45 KD (cytosolic).
- These findings indicate distinct mRNA populations for fumarase isoforms in different rat tissues.
Conclusions:
- Rat brain polysomes predominantly contain mRNA for the mitochondrial fumarase precursor.
- Rat liver polysomes contain mRNA for both mitochondrial and cytosolic fumarase precursors.
- The results support the known absence of cytosolic fumarase in the rat brain due to specific mRNA expression patterns.