Fig. 3. The loss of viability in scn1-17 coincides with aberrant mitosis. (A) The wild-type and scn1-17 cells were first arrested at the G1 phase under the nitrogen source starvation at 33°C, and then shifted to the complete YPD medium at 20°C. The DNA contents of wild-typ e and scn1-17 were determined by FACS analysis. In wild-type, the S phase (S) occurred from 6 to 12 hours, whereas, in scn1-17, the progression of S phase was delayed by 1.5 hours (6-13.5 hours). 1C indicates the DNA content of a haploid cell in G1 that has unreplicated DNA, whereas 2C indicates those of a G2 cell that has already replicated DNA once. (B) Upper panel: the cell viability (Viability%) and septation index (SI%) were measured after the release from the G1 arrest at various time points in wild-type and scn1 mutant cells. The scn1 mutant cells lost the viability during the passage through the first mitosis, with the concomitant increase of missegregation. Lower panel: the frequency of mitotic phenotype in scn1-17 was determined. Frequency (%) of chromosome missegregation in scn1 (displaced, separated daughter nuclei) was determined (lower panel).