Figure 4.

Mis4 is sensitive to HU and becomes lethal in the S-phase block induced by HU. (A) like Cdc2-3w cells mis4-242 cells failed to form colonies in the presence of 5 mm HU at 26°C. (B) FACS analysis indicating that replication was blocked (DNA content is 1C) for 6 hr in mis4-242 in the presence of 15 mm HU at 26°C. (C) Mutant cells elongated with the interphase single nucleus. Bar, 10 μm. (D) Viability of mutant cells blocked by 15 mm HU remained high for 6 hr at 26°C. (E–G) Mutant cells were nitrogen starved to cause arrest in G₁ at 26°C and then released in complete medium at 36°C in the presence or the absence of 15 mm HU. (E) The DNA content of mutant cells remained 1C for 7 hr in the presence of HU but increased to 2C after 4 hr in the absence of HU. (F) Mutant cells were elongated at 36°C in the presence of HU. (G) Viability of mutant cells decreased to 50% and 20% after 3 and 5 hr, respectively, in the absence of HU (○), whereas viability decreased to 50% and 20%, respectively, after 5 and 7 hr in the presence of HU (•). Mutant cells became inviable while the DNA content was still 1C.