Figure 4.

Fusion and spore production defect in pak1 mutants. (A) Wild-type and pak1 cocultures were incubated for 12 and 24 h on V8 medium. Cells were harvested, fixed, and stained with DAPI to visualize nuclei. DAPI and DIC images were merged to observe nuclear migration. At 12-h, nuclear migration (arrowhead) and mating filaments were detected in the wild-type cocultures. At 24 h, the initial mating filament cells had replicated to form dikaroytic filaments with clamp cells (asterisks), whereas in the pak1 coculture mating filaments were at the nuclear migration (arrowhead) stage of development. Bar, 10 μm. (B) Quantitative mating analysis. Bilateral crosses consisting of wild-type, pak1, and ste20 auxotrophic strains and prototrophic partners were prepared, incubated for 7 d on V8 medium, and serially diluted onto medium to select recombinants that were Ura^- and either Lys⁺ (ste20 cross) or Ade⁺ (pak1 cross). Top, progeny from the pak1 bilateral cross (left) and the ste20 bilateral cross (right). Bottom, progeny from the wild-type control cross for pak1 (left) and ste20 (right).