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The PMR2 gene cluster encodes functionally distinct isoforms of a putative Na+ pump in the yeast plasma membrane
J Wieland1, A M Nitsche, J Strayle
1Institut für Biochemie der Universität Stuttgart, Germany.
Abstract:
We report a structural and functional analysis of the PMR2 gene cluster in yeast. We found that several strains of Saccharomyces cerevisiae contain multiple PMR2 genes repeated in tandem, whereas most phylogenetically related yeasts appear to possess only a single PMR2 gene. This unusual tandem array of nearly identical genes encodes putative ion pumps involved in Na+ tolerance. Pmr2a and Pmr2b, the proteins encoded by the first two repeats, differ by only 13 amino acid exchanges. Both proteins share localization to the plasma membrane, but represent distinct isoforms of a putative Na+ pump. When expressed under identical conditions in vivo, Pmr2a and Pmr2b cause different tolerances to Na+ and Li+. Finally, we show that the Na+ tolerance mediated through these pumps is regulated by calmodulin via a calcineurin-independent mechanism which activates the Pmr2 ion pumps post-transcriptionally.
Insights
Yeast strains possess multiple PMR2 genes for sodium (Na+) tolerance, unlike related species. These genes encode distinct ion pumps regulated by calmodulin, enhancing Na+ and lithium (Li+) tolerance post-transcriptionally.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- The PMR2 gene cluster in yeast is crucial for ion homeostasis.
- Understanding the structure and function of PMR2 gene arrays is key to deciphering mechanisms of ion tolerance.
Purpose of the Study:
- To investigate the structural and functional characteristics of the PMR2 gene cluster in Saccharomyces cerevisiae.
- To elucidate the role of PMR2 gene duplication and its encoded proteins in sodium (Na+) and lithium (Li+) tolerance.
Main Methods:
- Comparative genomic analysis of PMR2 gene clusters across yeast species.
- Structural and functional characterization of PMR2 gene products (Pmr2a and Pmr2b).
- In vivo expression studies to assess Na+ and Li+ tolerance conferred by Pmr2a and Pmr2b.
Main Results:
- Saccharomyces cerevisiae strains exhibit tandem arrays of multiple PMR2 genes, whereas related yeasts typically have a single copy.
- The PMR2 gene array encodes putative ion pumps involved in Na+ tolerance, with Pmr2a and Pmr2b representing distinct isoforms.
- Pmr2a and Pmr2b exhibit differential effects on Na+ and Li+ tolerance when expressed in vivo.
- Calmodulin regulates Na+ tolerance mediated by Pmr2 ion pumps through a calcineurin-independent, post-transcriptional mechanism.
Conclusions:
- The duplication and tandem arrangement of PMR2 genes in yeast contribute to enhanced ion tolerance.
- Distinct Pmr2 isoforms play specific roles in mediating tolerance to Na+ and Li+.
- Calmodulin-dependent post-transcriptional regulation fine-tunes the activity of Pmr2 ion pumps for ion homeostasis.