The eukaryotic DNA damage checkpoint is a signal transduction pathway that delays entry into mitosis following DNA damage until the DNA damage is repaired. By phosphorylating key cell-cycle regulators, the protein kinase Chk1 links this checkpoint pathway with the cell-cycle machinery. On , Nancy Walworth and her team report that in fission yeast the accumulation of Chk1 in the nucleus after DNA damage depends on the interaction of Chk1 with Rad24, a 14-3-3 protein. Previous work has shown that 14-3-3 proteins, conserved multifunctional adaptors, preferentially associate with phosphorylated Chk1, which is produced in response to DNA damage. The authors now identify a stretch of leucine residues in Chk1 that is required for the interaction of Chk1 with Rad24, as well as its phosphorylation and localization to the nucleus after DNA damage. They also identify nuclear import and export sequences within Chk1 and propose that these sequences, in conjunction with 14-3-3 proteins, regulate Chk1 localization and function.
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