Expression of C-terminal truncations of Exo1 and sensitivity to DNA-damaging agents. (A) Intrinsic disorder prediction of Exo1 using the IUPred algorithm in which values above 0.5 indicate residues predicted to be intrinsically disordered and values below 0.5 to be ordered. The N-terminus, harboring conserved N- and I-nuclease domains, is predicted to be ordered, whereas the C-terminus, which appears devoid of enzymatic activity but contains phosphorylation sites and sites for interaction with mismatch repair proteins, is disordered. The sites at which the Exo1 truncations examined in this study terminate are indicted by vertical dotted lines. The location of conserved domains was adapted from reference : nuclease domains (orange boxes, 16-96 aa, 123-257 aa), Mlh1 interaction domain (green box, 400-702 aa) and the Msh2 interaction domain (blue box, 368-702 aa). Phosphorylation sites at S372, S567, S587 and S692, implicated in checkpoint regulation , are indicated by red asterisks. (B) Western blot analysis of expression of myc-epitope tagged exo1 truncations and wildtype Exo1. Molecular weight markers (kD) are indicated on the left. (C) Cells expressing Exo1 truncations lacking 280 or more C-terminal residues are as sensitive to 0.05% MMS as the exo1Δ mutant whereas cells expressing exo1 truncations lacking 260 or fewer C-terminal residues show wildtype levels of resistance to MMS. No sensitivity to 200 mM hydroxyurea was observed for any of the tested yeast strains.