| NIRF induces G 1 arrest and associates with Cdk 2 . ^^^ Immunoprecipitation and immunoblotting experiments showed that NIRF bound to the inactive Cdk 2 cyclin E complex . ^^^ There existed phosphorylated NIRF in cells , and dephosphorylated NIRF interacted with Cdk 2 . ^^^ NIRF was phosphorylated by Cdk 2 in vitro . ^^^ |