Figure 2.

Ctf18 is involved in the Cds1-dependent replication checkpoint. (A and B) Synergistic interaction of ctf18Δ and chk1Δ in UV and HU survival assays indicates that Ctf18 is required for cellular tolerance to fork arrest. For UV survival assays, fivefold serial dilution of cells were plated on YES agar medium and exposed to the indicated doses of UV. Agar plates were then incubated for 2–3 d at 32°C. For HU sensitivity assays, fivefold serial dilution of cells were incubated on YES agar medium supplemented with the indicated amounts of HU for 2–4 d at 32°C. Representative images of repeat experiments are shown. (C) Cds1 activation is strongly reduced in ctf18Δ cells. Cells of the indicated genotypes were incubated in YES liquid medium supplemented with 12 mM HU for 0, 1, 2, and 4 h at 30°C. Kinase activity of immunoprecipitated Cds1 was measured using MBP as a substrate. The radiolabeled MBP was detected after gel electrophoresis (top). The radioactivity levels (cpm) of MBP were then determined in a liquid scintillation counter (bottom). Representative results from repeat experiments are shown.