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The smt-0 mutation which abolishes mating-type switching in fission yeast is a deletion
U Styrkársdóttir1, R Egel, O Nielsen
1Institute of Genetics, University of Copenhagen, Denmark.
Abstract:
Mating-type switching in the fission yeast, S. pombe, is initiated by a DNA double-strand break (DSB) between the mat1 cassette and the H1 homology box. The mat1-cis-acting mutant, smt-0, abolishes mating-type switching and is shown here to be a 263-bp deletion. This deletion starts in the middle of the H1 homology box, 31 bp from the site of the DSB, and extends into the flanking region distal to mat1. The sequence of the region distal to H1 in the wild-type is also presented. In this region we observe a bias in the distribution of purine residues between the two DNA strands.
Insights
A specific DNA deletion in fission yeast (S. pombe) prevents mating-type switching by disrupting the DNA double-strand break site. This finding clarifies the mechanism of mating-type switching regulation.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Mating-type switching in S. pombe is a crucial process for sexual reproduction.
- This process is initiated by a programmed DNA double-strand break (DSB) at a specific locus.
- The mat1 locus and H1 homology box are key elements involved in this DSB formation.
Purpose of the Study:
- To investigate the molecular basis of the mat1-cis-acting mutant, smt-0.
- To understand how mutations in the H1 homology box affect mating-type switching.
- To identify the precise genetic alteration responsible for abolishing mating-type switching.
Main Methods:
- DNA sequencing to identify the mutation in smt-0.
- Analysis of the deletion's location relative to the DSB site and flanking regions.
- Sequence analysis of the wild-type region distal to H1.
Main Results:
- The smt-0 mutant is characterized by a 263-bp deletion.
- This deletion occurs within the H1 homology box, 31 bp from the DSB initiation site.
- The deletion extends into the region distal to the mat1 locus.
- A purine residue distribution bias was observed between DNA strands in the wild-type distal region.
Conclusions:
- The identified deletion in smt-0 directly impairs the DNA double-strand break required for mating-type switching.
- This deletion provides critical insight into the cis-acting elements regulating mating-type switching in S. pombe.
- The sequence analysis reveals potential regulatory features in the DNA flanking the mating-type locus.