Discription：Cyclin-dependent kinase inhibitors （CDKIs） are proteins that bind to and inhibit the activity of CDKs. Two major classes of CDK inhibitors have been identified. The p16 family （p15, p16, p18 and p19） binds to and inhibits the activities of CDK4 and CDK6. The p21 family （p21, p27, p28 and p57） can bind to broad range of CDK-cyclin complexes and inhibit their activities. CDKIs are capable of suppressing growth, and several lines of evidence strongly suggest that at least some CDKIs may be tumor suppressor proteins. p16-INK4A is the member of p16 family and is encoded by CDKN2A gene in humans. It has three isoforms, which are wildly expressed but not detected in brain or skeletal muscle, except that isoform 3 is pancreas-specific. Full-length human p16INK4a shares 63％ aa identity with mouse p16INK4a. Protein transduction using TAT fusion proteins represents an alternative methodology for introducing transcription factors and other nuclear proteins into primary, as well as transformed, cells. Recombinant Human p16-INK4a-TAT expressed in E. coli is an 18.0kDa protein containing 167 amino-acid residues, including the 155 residues of full-length p16-INK4a and a 12-residue C-terminal TAT peptide （GYGRKKRRQRRR） .
