Abnormal polarization of growth in pom1-Δ1 strains. (A) Strains 972 (wild type) and JB110 (pom1-Δ1) were grown at 36°C to 5 × 106 cells/ml, then stained with rhodamine–phalloidin to visualize F-actin organization. Strains JB20 (cdc25-22) and JB120 (pom1-Δ1 cdc25-22) were grown to the same titer at 25°C, then shifted to 36°C for 3 hr before staining. (B) Cells from the populations shown in A were scored for unipolar or bipolar actin localization, as were cells of strains SP622 (cdc10–V50) and JB121 (pom1-Δ1 cdc10–V50) (grown as described for the cdc25-22 strains in A). For strains 972 and JB110, the percentages of cells with an actin ring were also scored. In the other strains, these percentages were <5%. At least 250 cells of each strain were evaluated. (C) Strains SP622, JB121, JB20, and JB120 were grown at 25°C to 5 × 106 cells/ml, shifted to 36°C for 4 hr, and stained with Calcofluor. (D) Cells (⩾250) from each population shown in C were scored for the presence or absence of new-end growth.