WILD-TYPE ALTERNATIVELY SPLICED P53 - BINDING TO DNA AND INTERACTION WITH THE MAJOR P53 PROTEIN IN-VITRO AND IN CELLS

A p53 variant protein (p53as) generated from alternatively spliced p53 RNA is expressed in normal and malignant mouse cells and tissues, and p53as antigen activity is preferentially associated with the Gz phase of the cell cycle, suggesting that p53as and p53 protein may have dis tinct properties. Using p53as and p53 proteins translated bl vitro, we now provide evidence that p53as protein has efficient sequence-specif ic DNA-binding ability. DNA binding by p53 protein is inefficient in c omparison and requires activation. Furthermore, p53as and p53 proteins formed hetero-oligomers when co-translated ill vitro, resulting in in activation of p53as DNA-binding activity. Gel filtration indicated tha t p53as translated in vitro, like p53, formed tetramers. In support of a functional role of p53as in cells, p53as/p53 hetero-oligomers were coimmunoprecipitated from mouse cells, and both protein forms were det ectable in nuclear extracts by electrophoretic mobility shift assays. These results suggest that the biochemical functions of p53 are mediat ed by interaction between two endogenous protein products of the wild- type p53 gene.