Functional interaction of Purα with the Cdk2 moiety of cyclin A/Cdk2

Purα is a sequence-specific single-stranded nucleic acid-binding protein and a member of the highly conserved Pur family. Purα has been shown to colocalize with cyclin A/Cdk2 and to coimmunoprecipitate with cyclin A during S-phase. Here we show that this interaction is mediated by a specific affinity of Purα for Cdk2. In pull-down assays GST-Purα efficiently binds Cdk2 and Cdk1, binds Cdk4 less efficiently, and does not display binding to Cdk6. Purα stimulates several-fold the phosphorylation in vitro of histone H1 by cyclin A/Cdk2, produced from baculovirus constructs. Double chromatin immunoprecipitation using antibodies to Cdk2 and Purα reveals that both proteins colocalize in HeLa cells to DNA segments upstream of the c-MYC gene. Pur family member Purγ colocalizes with Cdk2 to a specific DNA segment in this region.