Lindsey Barron and Alexander J. R. Bishop
P53 is a globular protein with distinct domains and a key tumor suppressor that functions through transcriptional transactivation, repression and protein-protein interactions. Numerous studies have implicated protein-protein interactions between p53 and a multitude of cellular proteins with a variety of known functions. Because of these interactions, and the many gene expression regulations, a multitude of potential mechanisms and their relationship to tumor suppression have been proposed. It is desirable to test these interactions in an in vitro setting to demonstrate that any identified interaction is direct. Due to the difficulties associated with purifying recombinant full-length p53, many studies have utilized the p53 DNA binding domain to test for direct protein interactions with p53. The DNA binding domain of p53 is structured, folds independently and dictates the stability of the full-length protein. Therefore, it is reasonable to perform in vitro experiments with this isolated domain. However, we demonstrate that if a HIStag is present on the interacting partner when testing for an interaction with p53, this can lead to detection of an artefactual protein-protein interaction raising the possibility of false positive results. Furthermore, the presence of the HIS-tag promotes aggregation and precipitation of the p53 DNA binding domain.