Abstract
Cells of homothallic strains of Schizosaccharomyces pombe efficiently switch between two mating types called P and M. The phenotypic switches are due to conversion of the expressed mating-type locus (mat1) by two closely linked silent loci, mat2-P and mat3-M, that contain unexpressed information for the P and M mating types, respectively. In this process, switching-competent cells switch to the opposite mating type in 72-90% of the cell divisions. Hence, mat2-P is a preferred donor of information to mat1 in M cells, whereas mat3-M is a preferred donor in P cells. We investigated the reason for the donor preference by constructing a strain in which the genetic contents of the donor loci were swapped. We found that switching to the opposite mating type was very inefficient in that strain. This shows that the location of the silent cassettes in the chromosome, rather than their content, is the deciding factor for recognition of the donor for each cell type. We propose a model in which switching is achieved by regulating accessibility of the donor loci, perhaps by changing the chromatin structure in the mating-type region, thus promoting an intrachromosomal folding of mat2 or mat3 onto mat1 in a cell type-specific fashion. We also present evidence for the involvement of the Swi6 and Swi6-mod trans-acting factors in the donor-choice mechanism. We suggest that these factors participate in forming the proposed folded structure.
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Selected References
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- Arcangioli B., Klar A. J. A novel switch-activating site (SAS1) and its cognate binding factor (SAP1) required for efficient mat1 switching in Schizosaccharomyces pombe. EMBO J. 1991 Oct;10(10):3025–3032. doi: 10.1002/j.1460-2075.1991.tb07853.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Beach D. H., Klar A. J. Rearrangements of the transposable mating-type cassettes of fission yeast. EMBO J. 1984 Mar;3(3):603–610. doi: 10.1002/j.1460-2075.1984.tb01855.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bresch C., Müller G., Egel R. Genes involved in meiosis and sporulation of a yeast. Mol Gen Genet. 1968;102(4):301–306. doi: 10.1007/BF00433721. [DOI] [PubMed] [Google Scholar]
- Egel R., Beach D. H., Klar A. J. Genes required for initiation and resolution steps of mating-type switching in fission yeast. Proc Natl Acad Sci U S A. 1984 Jun;81(11):3481–3485. doi: 10.1073/pnas.81.11.3481. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Heyer W. D., Sipiczki M., Kohli J. Replicating plasmids in Schizosaccharomyces pombe: improvement of symmetric segregation by a new genetic element. Mol Cell Biol. 1986 Jan;6(1):80–89. doi: 10.1128/mcb.6.1.80. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ito H., Fukuda Y., Murata K., Kimura A. Transformation of intact yeast cells treated with alkali cations. J Bacteriol. 1983 Jan;153(1):163–168. doi: 10.1128/jb.153.1.163-168.1983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kelly M., Burke J., Smith M., Klar A., Beach D. Four mating-type genes control sexual differentiation in the fission yeast. EMBO J. 1988 May;7(5):1537–1547. doi: 10.1002/j.1460-2075.1988.tb02973.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Klar A. J., Bonaduce M. J. swi6, a gene required for mating-type switching, prohibits meiotic recombination in the mat2-mat3 "cold spot" of fission yeast. Genetics. 1991 Dec;129(4):1033–1042. doi: 10.1093/genetics/129.4.1033. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Klar A. J. The developmental fate of fission yeast cells is determined by the pattern of inheritance of parental and grandparental DNA strands. EMBO J. 1990 May;9(5):1407–1415. doi: 10.1002/j.1460-2075.1990.tb08256.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- LEUPOLD U. Studies on recombination in Schizosaccharomyces pombe. Cold Spring Harb Symp Quant Biol. 1958;23:161–170. doi: 10.1101/sqb.1958.023.01.020. [DOI] [PubMed] [Google Scholar]
- Lorentz A., Heim L., Schmidt H. The switching gene swi6 affects recombination and gene expression in the mating-type region of Schizosaccharomyces pombe. Mol Gen Genet. 1992 Jun;233(3):436–442. doi: 10.1007/BF00265441. [DOI] [PubMed] [Google Scholar]
- Moreno S., Klar A., Nurse P. Molecular genetic analysis of fission yeast Schizosaccharomyces pombe. Methods Enzymol. 1991;194:795–823. doi: 10.1016/0076-6879(91)94059-l. [DOI] [PubMed] [Google Scholar]
- Munz P., Leupold U. Gene conversion in nonsense suppressors of Schizosaccharomyces pombe. I. The influence of the genetic background and of three mutant genes (rad2, mut1 and mut2) on the frequency of the post-meiotic segregation. Mol Gen Genet. 1979 Feb 26;170(2):145–148. doi: 10.1007/BF00337789. [DOI] [PubMed] [Google Scholar]
- Nielsen O., Egel R. Mapping the double-strand breaks at the mating-type locus in fission yeast by genomic sequencing. EMBO J. 1989 Jan;8(1):269–276. doi: 10.1002/j.1460-2075.1989.tb03373.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ruusala T. The mating type in fission yeast is switched independently of its expression. Curr Genet. 1991 Nov;20(5):379–383. doi: 10.1007/BF00317065. [DOI] [PubMed] [Google Scholar]
- Singh J., Klar A. J. DNA polymerase-alpha is essential for mating-type switching in fission yeast. Nature. 1993 Jan 21;361(6409):271–273. doi: 10.1038/361271a0. [DOI] [PubMed] [Google Scholar]
- Thon G., Klar A. J. The clr1 locus regulates the expression of the cryptic mating-type loci of fission yeast. Genetics. 1992 Jun;131(2):287–296. doi: 10.1093/genetics/131.2.287. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weiler K. S., Broach J. R. Donor locus selection during Saccharomyces cerevisiae mating type interconversion responds to distant regulatory signals. Genetics. 1992 Dec;132(4):929–942. doi: 10.1093/genetics/132.4.929. [DOI] [PMC free article] [PubMed] [Google Scholar]