Methods to study p53-repressed promoters.

There is substantial evidence in the literature that, in addition to functioning as an activator of transcription, the p53 tumor suppressor protein can also function as a sequence-specific transcriptional repressor of a separate set of genes. However, elucidation of the mechanism whereby p53 functions as a transcriptional repressor has been obscured by the use of artificial assays to measure this activity; these assays include transient transfection analyses, where both p53 and target promoters are overexpressed. This chapter describes alternative approaches for the definition of sequence elements that mediate transcriptional repression by p53. These include the McKay (immunobinding) assay, which measures the in vitro binding of large fragments of DNA, as well as chromatin immunoprecipitations (ChIPs), which measure in vivo binding. The use of such assays should better define the mechanism of transcriptional repression by p53 and should aid in the elucidation of the contribution of this activity to p53-dependent growth arrest and programmed cell death (apoptosis).