Whole cell extracts were obtained by solubilizing cells in lysis buffer (20 mM Tris pH 7.4, 150 mM NaCl, 1% Triton X-100, 1 mM EDTA, 1 mM ethylene glycol tetraacetic acid (EGTA), plus Complete protease inhibitors and PhosSTOP (Roche Diagnostics)). Lysates were clarified by centrifugation at 16,000g for 15 min.