IDENTIFICATION OF CDK2 BINDING-SITES ON THE P27(KIP1) CYCLIN-DEPENDENT KINASE INHIBITOR

A cdk2 binding domain on p27(Kip1) located within the sequence of amin o acids 53-85 was further characterized by generating a series of poin t mutations within amino acid residues 62-75. Two regions, FDF (residu es 62-64) and GXY (residues 72 and 74), were identified within the bet a hairpin region of p27(Kip1)., Mutations within these regions essenti ally completely inhibited the binding to ill,, vitro translated cdk2 a nd cdk2/cyclin E complexes formed in vitro or iii vivo., The p27(Kip1) GST-fusion protein of the point mutation that replaces phenylalanine at residue 64 to alanine (F64A) showed approximately twofold less inhi bition of cdk2 kinase activity. The cellular response to the introduct ion of the F64A mutant form of p27(Kip1) was compared to that of p27(K ip1) wild type by transfecting HeLa cells with constructs of full leng th sense and antisense coding sequences, Overexpression of the F64A mu tant form of p27(Kip1) bound significantly lower levels of cdk2 as com pared to wild type and did not effect the cdk2 related kinase activity of the transfected HeLa cells. Overexpression of wild type p27(Kip1) resulted in a reduction of the level of cdk2 kinase activity and effec tively suppressed the growth of the transfected HeLa cells.