Binding of 14-3-3 proteins and nuclear export control the intracellular localization of the mitotic inducer Cdc25

Binding of 14-3-3 proteins near the nuclear localization sequence of Xenopu s Cdc25 suppresses its ability to induce entry into mitosis. We have examin ed the intracellular localization of green fluorescent protein (GFP)-tagged wild-type Cdc25 or a mutant (S287A) that cannot bind 14-3-3 proteins. Upon coexpression with Myc-14-3-3 epsilon, GFP-Cdc25-WT was predominantly cytop lasmic, whereas GFP-Cdc25-S287A was exclusively nuclear. Leptomycin B, an i nhibitor of nuclear export, elicited a prompt redistribution of GFP-Cdc25-W T to the nucleus. Mutagenesis experiments demonstrated that Cdc25 contains multiple nuclear export sequences. These studies indicate that the binding of 14-3-3 proteins and nuclear export regulate the intracellular localizati on of Cdc25.