WEE1 is located in the nucleus where it phosphorylates and inactivates different forms of CycB1/CDC2 (Heald et al., 1993). CDC25C can be found in the cytoplasm and in the nucleus and activates the complex (Liu et al., 1999; Liu et al., 1997; Vermeulen et al., 2003). CDC25C responds to DNA damage via the phosphorylation by CHEK1 and CHEK2 (Castedo et al., 2002). The modified CDC25C is then exported to the cytoplasm preventing the activation of nuclear CycB1/CDC2 (Vermeulen et al., 2003). In a positive feedback already described, CycB1/CDC2 activates CDC25C, through phosphorylation which, in turn, activates the CDK complex through dephosphorylation. CDC25C activity is low during interphase and high during mitosis whereas WEE1 activity has an opposite behaviour.
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