p21: structure and functions associated with cyclin-CDK binding.

The cyclin dependent kinase inhibitor, p21, is a multifunctional protein involved in coordinating the cellular response to negative growth signals. Induced by cellular damage under the transcriptional control of the p53 tumour suppressor protein, p21 interfaces with a number of cellular proteins involved in growth control. Although p21 has a diverse range of activities, from assembly factor to transcriptional modulator, its ability to interact with and regulate the activity of the cyclin dependent protein kinases is paramount to many of these functions.