ATM phosphorylates BRCA1 at serine residues S1387, S1423, S1457, and S1524 (Cortez et al. 1999, Gatei et al. 2000). At least a fraction of these sites and some additional BRCA1 SQ/TQ sites can also be phosphorylated by ATR (Tibbetts et al. 2000). ATM also phosphorylates BARD1, the heterodimerization partner of BRCA1, at threonine residues T714 and T734 (Kim et al. 2006).