Figure 6.

The rfc3-1 mutant is sensitive to HU, MMS, and gamma and UV irradiation at permissive temperature. Ten micromolar HU (A) or 0.007% MMS (B) was added to the exponentially growing rfc3-1 (MSY1), wild-type, and rad3Δ cells at 28°C (time = 0), and incubation was continued. After 3, 6, 9, and 12 h, cells were collected, diluted, plated, and further incubated at 28°C for 4 d. Colonies were scored, and viability was expressed as a percentage of the colonies that formed on samples plated immediately before addition of HU or MMS. Cell morphology was monitored with a microscope after these treatments for 12 h (A and B, right). In the rfc3-1 mutant, abnormal nuclear divisions were detected as shown by arrows. Bar, 10 μm. (C) For gamma irradiation, cells were grown to early log phase in the YPD medium, removed, diluted, and irradiated by gamma rays from a ⁶⁰Co source at a dose rate of 234 Gy/h. After irradiation, appropriately diluted samples were plated and incubated at 28°C for 4 d, when the survival rates were measured by counting the colonies. (D) For UV irradiation, freshly grown cells were spread on YPD plates, and the plates were immediately exposed to the appropriate dose of UV irradiation. The survival rates were measured by counting the colonies after a 4-d culture at 28°C.