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The fission yeast gene pmt1+ encodes a DNA methyltransferase homologue
C R Wilkinson1, R Bartlett, P Nurse
1Institute of Cell and Molecular Biology, University of Edinburgh, UK.
Abstract:
DNA methylation of cytosine residues is a widespread phenomenon and has been implicated in a number of biological processes in both prokaryotes and eukaryotes. This methylation occurs at the 5-position of cytosine and is catalyzed by a distinct family of conserved enzymes, the cytosine-5 methyltransferases (m5C-MTases). We have cloned a fission yeast gene pmt1+ (pombe methyltransferase) which encodes a protein that shares significant homology with both prokaryotic and eukaryotic m5C-MTases. All 10 conserved domains found in these enzymes are present in the pmt1 protein. This is the first m5C-MTase homologue cloned from a fungal species. Its presence is surprising, given the inability to detect DNA methylation in yeasts. Haploid cells lacking the pmt1+ gene are viable, indicating that pmt1+ is not an essential gene. Purified, bacterially produced pmt1 protein does not possess obvious methyltransferase activity in vitro. Thus the biological significance of the m5C-MTase homologue in fission yeast is currently unclear.
Insights
Researchers identified a cytosine-5 methyltransferase (m5C-MTase) homolog in fission yeast, pmt1+. Despite homology to known enzymes, its biological role and in vitro activity remain unclear, posing a puzzle in yeast epigenetics.
Area of Science:
- Epigenetics
- Molecular Biology
- Yeast Genetics
Background:
- DNA methylation at the 5-position of cytosine is catalyzed by cytosine-5 methyltransferases (m5C-MTases) and is crucial in various biological processes.
- The presence and function of m5C-MTases have been extensively studied in prokaryotes and eukaryotes, but not in fungi.
Purpose of the Study:
- To clone and characterize a potential DNA methyltransferase from the fission yeast Schizosaccharomyces pombe.
- To investigate the homology and potential function of the cloned gene in relation to known m5C-MTases.
Main Methods:
- Cloning of the fission yeast gene pmt1+ (pombe methyltransferase).
- Bioinformatic analysis to compare pmt1+ protein homology with known m5C-MTases.
- Gene deletion studies in haploid fission yeast cells.
- In vitro methyltransferase activity assays using purified pmt1+ protein.
Main Results:
- The fission yeast gene pmt1+ was cloned, encoding a protein with significant homology to both prokaryotic and eukaryotic m5C-MTases, including all 10 conserved domains.
- This represents the first cloned m5C-MTase homolog from a fungal species.
- Haploid cells lacking pmt1+ were viable, indicating it is not essential for cell survival.
- Purified pmt1+ protein showed no detectable methyltransferase activity in vitro.
Conclusions:
- Fission yeast possesses a homolog of cytosine-5 methyltransferases (pmt1+), despite the lack of detectable DNA methylation in yeasts.
- The biological significance of this m5C-MTase homolog in fission yeast is currently unknown.
- Further research is needed to elucidate the function of pmt1+ and its role in the absence of detectable DNA methylation.