Fig. 4.

A conserved 15-amino-acid peptide (CT15) is sufficient to stimulate MRN endonuclease activity. (A) Location of CT15 in reference to the full length Ctp1. (B) Endonuclease activity of MR was assayed in the presence of CT15 peptides. (C) Same as B except that MRN was used. (D) Same as B but CT15 variants mutated at conserved amino acids were used at 100 µM. (E) A synthetic peptide of the human CT15 counterpart (hCT15e) stimulates hMRN endonuclease activity when its CDK and ATM target sites (Thr-847 and Thr-859, respectively) are phosphorylated. In this assay, hMRN was introduced at 100 nM with respect to the concentration of RAD50 as a monomer. The peptides were used at 50 µM, and potassium chloride, instead of sodium chloride, was used at 100 mM.