Cells and colonies of the homothallic (h90) strains, WT(JY4)/pREP42, gaf1Δ(KL211)/pREP42, WT(JY4)/pREP-Gaf1, and gaf1Δ(KL211)/pREP-Gaf1, were analyzed for sporulation by DIC microscopy and iodine staining, respectively. (A) Cells were grown to mid-log phase in EMM2 for 18 h and shifted to EMM-N medium. Samples were taken from the cultures at intervals, and the morphological characteristics of cells were observed by DIC microscopy. Bar, 10 µm. (B) Cells were grown to mid-log phase in EMM2 for 18 h and spotted onto EMM-N plates with (+B1) or without (−B1) 20 µM thiamine. Sporulation was monitored by iodine vapor staining of colonies after 3-d incubation at 30°C. The FM value presented under each panel was determined by observing the cells under a DIC microscope. The values represent the average of at least three independent assays carried out in triplicate. WT denotes the wild-type (gaf1+).