Immunoblotting of RAD9 (phospho S1260) polyclonal antibody ( Cat # PAB11310 ) to yeast RAD9 at pS1260 was usedat a 1 : 200 dilution incubated overnight at 4°C to detect RAD9 by Western blot. Lanes were loaded with 50 ng each of recombinant GST fusion protein containing S. cerevisiae RAD9 ( amino acids 991-1309, ~60 kDa ) on a 4-20% Criterion gel for SDS-PAGE. Lane 1, non-phosphorylated wild type yeast RAD9. Lane 2, in vitro phosphorylated wild type yeast RAD9. Lane 3, non-phosphorylated S1129A/S1260A double mutant RAD9. Lane 4, in vitro phosphorylated S1129A/S1260A double mutant. Phosphorylation of RAD9 was by treatment with ATP and RAD53 kinase. RAD53 kinase autophosphorylates and appears cross reactive as it is detected on the blot as 90 and 110kDa bands ( asterisk ).