Extended Data Fig. 9: Structural analysis and comparisons of Mec1.

a-c, Electron density of the activation loop from the apo (a), AMP-PNP-bound (b) and AMP-PNP-bound F2244L mutant (c), showing that in all cases the activation loop remains ordered, with flexibility around the DFD-motif (asterisks), which could not be easily resolved in the wild-type structures. Several large residues are shown as landmarks. d,e, PRD-I hydrophobic network comparisons between Mec1-Ddc2 (e) and Tel1 (e), suggesting that M2312 plays an analogous role to W2701 in Tel1. PRD-I, activation loop and catalytic loop are colored as in Fig. 1b. f-i, Comparison of stabilizing interactions in activations loops across PIKKs. f, In Mec1, the DFD+1 residue plays a role in stabilizing the activation loop. In our activated structure the thiol group of the invariant C2246 forms an H-bond with the main chain carbonyl of L2222 of the catalytic loop, helping to stabilize the active state. In Tel1 the DLG+1 (I2634) forms a hydrophobic spline with G2639 and L2642 of the activation loop (g), whereas in mTOR (h) and DNA-PKcs (i) an ion pair is preferred.