Hyperspeckled mutants of Schizosaccharomyces pombe: frequent mating-type switching without detectable double-strand breaks |
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Authors: | Holger Michael Hans-Christian Fecke Oliver Fleck and Herbert Gutz |
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Institution: | (1) Institut für Genetik, Technische Universität Braunschweig, Postfach 33 29, D-38023 Braunschweig, Germany;(2) Present address: Institut für Allgemeine Mikrobiologie, Baltzer Str. 4, CH-3012 Bern, Switzerland |
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Abstract: | Mating-type (MT) switching in homothallic (h>
90
) strains of Schizosaccharomyces pombe is initiated by a DNA double-strand break (DSB) at the distal end of the expression cassette mat1. The cis-acting smt-s1 mutation C13-P11 reduces the frequency of MT switching. It is a small deletion mapping approximately 50 by distal to the site of the DSB. From the h
90
smt-s1 strain we isolated 13 mutants with a hyperspeckled iodine reaction. In these mutants the frequency of MT switching is increased. The mutations define nine different hsp genes, none of which maps in or close to the MT region. We tested one mutant of each gene for the presence of DSBs at mat1. Curiously, in none of the h
90
smt-s1 hsp strains could DSBs be detected, although some sporulate nearly as efficiently as the h
90
smt-n wild type. The hsp mutations show no effect in smt-0 strains; the smt-0 deletion abolishes MT switching completely. Furthermore, we tested the interaction of hsp1-1 with swi1, swi2 and swi7 mutations. hsp1-1 has no effect in swi2 strains, whereas it increases MT switching in swi7 and, to a lesser degree, in swi1 mutants. |
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Keywords: | Schizosaccharomyces pombe Mating-type switching Double-strand break hsp mutations |
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