Interaction of checkpoint kinase 1 and the X-linked inhibitor of apoptosis during mitosis.

We report here that the checkpoint kinase Chk1 and the inhibitor of apoptosis protein (IAP) family member XIAP can be found in a complex in association with condensed chromosomes aligned at the metaphase plate during mitosis. The interaction between Chk1 and XIAP was transient and followed the breakdown of the nuclear envelope. Chk1 and XIAP also formed a complex in vitro and in coimmunoprecipitation experiments. The interaction between Chk1 and the BIR3 domain of XIAP in vitro required an N-terminal sequence in Chk1 that is identical to the BIR-binding motif at the N-terminus of HID. An interaction of Chk1 and XIAP may imply a mechanism of coupling between the regulatory networks that control cell cycle progression and apoptosis during mitosis.