Figure 2. Mre11 is phosphorylated at SQ/TQ motifs in response to DSBs.

(A) The amino acid sequences of Mre11 proteins from Homo sapiens (ACcession number: P49959), Mus musculus (AC: Q61216), Gallus gallus (AC: Q9IAM7), and Xenopus laevis (AC: Q9W6K1) were aligned using the CLUSTAL W (1.83) multiple sequence alignment program. SQ/TQ motifs are highlighted in bold. The amino acid positions of the Ser/Thr residues in the eight SQ/TQ motifs of the human protein are indicated. ND: Nuclease domain; DBD-1/2: DNA-binding domain 1/2. (B) Purified MRN-WT, MRN-SA, and MRN-SD complexes were immunoprecipitated with preimmune (Pre) or anti-XMre11 (αMre11) serum, and the immunoprecipitates were immunoblotted with anti-hRad50 serum (upper panel), anti-hNbs1 serum (middle panel), and anti-XMre11 serum (lower panel). The inputs shown are equivalent to 15% of the purified MRN complex used in the co-immunoprecipitation reactions. (C) Mre11-depleted membrane-free extracts supplemented with recombinant MRN-WT or MRN-SA complex were incubated for 15 min in the presence or absence of DSBs (4.34 × 10¹⁰ ends/μl), okadaic acid (OA; 4 μM), and KU55933 (10 or 100 μM) or caffeine (10 mM), and analysed by Western blotting with anti-XMre11 serum.