In this project we have been looking for proteins binding to phosphorylated sites in DNA repair proteins. Previously, we and others have used peptide-pull down assays as a direct means of attributing specific binding functions to known sites phosphorylated by CK2 in DDR proteins. We have now applied the approach to identify proteins binding to four in vivo phosphorylated sites from DDR proteins RAD50 (Thr690), BRCA1 (Ser1336), MLH1 (Ser477) and XPC (Ser883, 884). These sites are conserved, reside within consensus sites for CK2, share similar sequence features, are mutated in cancer and/or their phosphorylation is known to affect (or is affected) by the DDR. We designed biotinylated 20 amino acid (aa) peptides encompassing the specific phosphorylated amino acids of BRCA1, RAD50, MLH1 and XPC that were either non-phosphorylated or phosphorylated. The biotinylated peptides were coupled to streptavidin beads and used to pull down proteins from HeLa nuclear extracts. Proteomic analysis revealed that all four sites bind proteins in a phospho-dependent manner. Each of the phosphorylated sites were binding various proteins including those implicated in DDR and cell cycle regulation as well as proteins involved in other cellular processes; some of these proteins have already known phospho-binding domains, while others do not. Interestingly, microtubule associated protein MAP7 featured prominently in all of the phosphorylated RAD50, BRCA1, MLH1 and XPC peptide pull-downs and MAP7 paralogue MAP7D1 also featured in the phosphorylated BRCA1 peptide pull-down. In the rest of the project we study the interactions and their function in DNA repair.