Fig. 2.
Stimulation of Mre11 endonuclease activity by Ctp1 is enhanced by Cka1 phosphorylation in the presence of Nbs1. (A) Substrate used for assaying Mre11 endonuclease activity. (B) MRN endonuclease activity was assayed with phosphorylated (red “p”) or unphosphorylated Ctp1. ND, an MRN complex containing nuclease-deficient Mre11H134S. (C) Titration of unphosphorylated Ctp1 (Ctp1) and phosphorylated Ctp1 (Ctp1p) in the endonuclease assay. Error bars, SD; n = 3. n/d, not determined. A representative gel image is shown in SI Appendix, Fig. S3. (D) Mre11 endonuclease activity in assays involving the Mre11-Rad50 complex and full-length or truncated Ctp1. (E) The effect of substitutions in the CxxC and RHR motifs on MRN endonuclease stimulation. Ctp1 (WT, truncated, or mutant proteins) is at 3 µM in D and E.