Cells take a break when they are TIAR ed

Cell cycle progression relies on controlled transition from one phase of the cell cycle to the next, and sensing whether or not a certain cell cycle phase has been completed before the next phase is allowed to start is crucial for genome integrity and cell survival. In this issue of EMBO Reports , Lafarga et al [1][Lafarga V, 2019] report an original mechanism for spatio‐temporal control of CDK 1 activity, which depends on a nuclear function of the RNA ‐binding protein TIAR . The role of TIAR to restrain mitotic onset is linked to a newly discovered membraneless compartment, termed G2/M transition granule ( GMG ), which transiently sequesters CyclinB‐ CDK 1 in response to replication stress to curb CDK 1 kinase activity and thereby tune G2 duration and mitotic commitment.