TRRAP-mediated regulation of Wee1

The G2 DNA damage checkpoint inhibits Cdc2 and mitotic entry through the dual regulation of Wee1 and Cdc25 by the Chk1 effector kinase. Up-regulation of Chk1 by mutation or overexpression bypasses the requirement for up-stream regulators or DNA damage to promote a G2 cell cycle arrest. We screened in fission yeast for mutations that rendered cells resistant to overexpressed Chk1. We identified a mutation in tra1, which encodes one of two homologs of TRRAP, an ATM/R-related pseudokinase that scaffolds several histone acetyltransferase (HAT) complexes. Inhibition of histone deacetylases reverts the resistance to overexpressed Chk1, suggesting this phenotype is due to a HAT activity, though expression of checkpoint and cell cycle genes is not greatly affected. Cells with mutant or deleted tra1 activate Chk1 normally and are checkpoint proficient. However, these cells are semi-wee even when overexpressing Chk1, and accumulate inactive Wee1 protein. The Cdr (changed division response) kinases Cdr1 and Cdr2 are negative regulators of Wee1, and while best characterized in the cellular response to limited nutrition, we show that they are required for the Tra1-dependent alterations to Wee1 function. This identifies Tra1 as another component controlling the timing of entry into mitosis via Cdc2 activation. Two and three independent microaaray experiments were done for wild type and the mutant (tra1-1) respectively.