To find the Mec1 targets that are responsible for mec1-100 suppression on HU, we performed a quantitative phosphoproteomic study. Specifically, we screened for modifications that are downregulated in mec1-100, compensated by pph3delta, and left unaffected by rad53delta. To eliminate contributions from Tel1, we used a tel1delta mec1-100 double mutant in the screen. Prior to extraction of proteins, the cultures were arrested in G1 by alpha-factor and released into S phase in the presence of HU. Samples were analyzed in triplicates.