FIG. 3.

Overproduction of Ndt80 allows activation of middle sporulation gene promoters in an ime2 mutant but does not promote spore formation. Wild-type cells (IME2/IME2) or ime2 mutants (ime2/ime2) harboring an SPS4-LacZ reporter gene were transformed with vector plasmid YCplac111 (vector), a high-copy plasmid carrying NDT80 (YEpNDT80), YCplac111 expressing NDT80 under the regulation of an IME2 promoter (IME2-NDT80), or YCplac111 expressing NDT80 under the regulation of a CUP1 promoter (CUP1-NDT80). The transformed cells were induced to sporulate, and 6 h following the induction of sporulation, β-galactosidase activity was assayed and expressed as Miller units (filled boxes). In cells that carry CUP1-NDT80, the expression of Ndt80 was induced at time zero by the addition of CuSO₄ to the medium to a final concentration of 100 μM. After 24 h in SPM, the cultures were microscopically examined for the percentage of cells that had formed asci (open boxes).