CHEK1 and chronic myelogenous leukemia, BCR-ABL1 positive: RAD51 has a number of different phosphorylation sites;15 it is phosphorylated at Tyrosine-315 by C-ABL, and this increased the nuclear translocation and foci formation ability of RAD51 in chronic myeloid leukemia cells.16 CHK1 phosphorylates RAD51 at Threonine-309, and this phosphorylation is necessary for HR repair; as expression of a phosphorylation-deficient mutant or inhibition of CHK1 sensitized the cells to DNA damage.17, 18 Having seen a decrease in foci formation in PLAURsi cells, we studied if impaired phosphorylation of RAD51 was the reason behind this observation.