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Separate information required for nuclear and subnuclear localization: additional complexity in localizing an enzyme
A M Rose1, P B Joyce, A K Hopper
1Department of Biochemistry, University of Louisville School of Medicine, Kentucky 40292.
Molecular and Cellular Biology
|December 1, 1992
Summary
The TRM1 gene product, N2,N2-dimethylguanosine-specific tRNA methyltransferase (m2(2)Gtase), targets both nuclei and mitochondria. Nuclear periphery localization requires complex signals beyond simple nuclear targeting sequences.
Area of Science:
- * Cellular and Molecular Biology
- * Biochemistry and Genetics
Background:
- * The TRM1 gene in Saccharomyces cerevisiae encodes N2,N2-dimethylguanosine-specific tRNA methyltransferase (m2(2)Gtase).
- * This enzyme functions in both the nucleus and mitochondria, indicating a dual localization.
- * Previous studies suggest specific targeting signals direct proteins to cellular compartments.
Purpose of the Study:
- * To identify the specific sequences responsible for targeting m2(2)Gtase to the nucleus and mitochondria.
- * To investigate the subnuclear localization requirements for m2(2)Gtase.
- * To understand the functional implications of mislocalizing m2(2)Gtase within the cell.
Main Methods:
- * Immunofluorescent staining to visualize m2(2)Gtase localization within yeast cells.
- * Genetic manipulation to alter sequences potentially involved in protein targeting.
- * Analysis of protein import into mitochondria and nuclei using truncated or modified proteins.
Main Results:
- * m2(2)Gtase localizes to the nuclear periphery, suggesting specific nuclear membrane association.
- * Nuclear import signals (e.g., KKSKKKRC) are necessary but not sufficient for correct subnuclear localization.
- * Mitochondrial import depends on N-terminal amino acids; removal of the first 48 amino acids abolishes mitochondrial import.
- * Truncated proteins lacking mitochondrial targeting are still imported into the nucleus but exhibit uniform distribution, not peripheral localization.
- * Mislocalization to the cytoplasm does not abolish the enzyme's biological function.
Conclusions:
- * Nuclear targeting of m2(2)Gtase involves complex signals beyond simple nuclear localization sequences, mediating association with the nuclear periphery.
- * Mitochondrial import relies on specific N-terminal sequences, similar to other well-characterized mitochondrial proteins.
- * Shared enzymes like m2(2)Gtase may utilize common import pathways for different organelles, but precise localization within an organelle can be complex.