The DNA binding activity of p53 displays reaction-diffusion kinetics

Abstract

The tumor suppressor protein p53 plays a key role in maintaining the genomic stability of mammalian cells and preventing malignant transformation. In this study, we investigated the intracellular diffusion of a p53-GFP fusion protein using confocal fluorescence recovery after photobleaching.Weshow that the diffusion of p53-GFP within the nucleus is well described by a mathematical model for diffusion of particles that bind temporarily to a spatially homogeneous immobile structure with binding and release rates k1 and k2, respectively. The diffusion constant of p53-GFP was estimated to be Dp53-GFP = 15.4 μm2 s-1, significantly slower than that of GFP alone, DGFP = 41.6 μm2 s -1. The reaction rates of the binding and unbinding of p53-GFP were estimated as k1 = 0.3 s-1 and k2 = 0.4 s -1, respectively, values suggestive of nonspecific binding. Consistent with this finding, the diffusional mobilities of tumor-derived sequence-specific DNA binding mutants of p53 were indistinguishable from that of the wild-type protein. These data are consistent with a model in which, under steady-state conditions, p53 is latent and continuously scans DNA, requiring activation for sequence-specific DNA binding. © 2006 by the Biophysical Society.