Construction of an h ^+Sstrain of Schizosaccharomyces pombe

Summary

By spontaneous in vivo integration of a mat2:1° plasmid, containing a Plus (P) cassette, into an h ^-LMT region of Schizosaccharomyces pombe an h ⁺ strain was obtained which neither mutates to h ^- nor to h ⁹⁰. Southern blotting showed that it possesses the same mating-type (MT) configuration as h ^-S except that P information resides in both cassettes. Therefore the strain was called h ^+S. By crossing h ^+S with the h ^- strain LK42 of Engelke et al. (1987) it was possible to obtain h ^- recombinants with the MT configuration mat1:1(M)smt-o-L-mat2:3(P). Because of the totally defective smt signal (smt-o) in these recombinants no MT switching occurs, so that M information is conserved in mat1:1; furthermore the cassette mat2:3(P) is not expressed like in strains with a K region. This proves that the K region does not cause the silencing of mat2:3(P).