Fig. 1. top3-134 mutants accumulate defects during S phase. Wild type (top3⁺) and top3-134 cells were arrested in G1 by nitrogen starvation and released into nitrogen-rich medium to restart the cell cycle at the non-permissive temperature of 36°C. Cells harvested at hourly intervals were processed for flow cytometry (A), and mitotic index was assessed by scoring bi-nucleate cells (B). The percentage of cells displaying aberrant mitosis with chromosomes lagging between the separating daughter nuclei (indicated by arrowheads in D) was also determined (C). (D) Fluorescence micrographs of DAPI-stained wild type and top3-134 cells, 6 hours after release from nitrogen starvation at 36°C. Bar, 10 µm.