CTF18-RLC is not required for DNA damage checkpoint activation, whereas elg1 mutants fail to activate Rad53 kinase. (A) Level of Rad53 phosphorylation in WT, Δelg1, Δddc1 Δctf18, and Δctf18 cells after induction of both checkpoint fusions, as indicated. Actin was used as a loading control for each Western blot. (B) Level of Rad53 phosphorylation in Δelg1, elg1-sim+386/7 DD, and elg1-S112A cells after induction of Ddc1-GFP-LacI and Ddc2-GFP-LacI as described in the Fig. 2B legend. Actin was used as a loading control.