P53 serine 392 phosphorylation increases after UV through induction of the assembly of the CK2•hSPT16•SSRP1 complex

Previously, we purified a UV-responsive p53 serine 392 kinase from F9 and HeLa cells and found that its activity is attributed to a high molecular weight protein complex containing the protein kinase CK2, along with the chromatin-associated factors hSPT16 and SSRP1. Here we determine that these proteins interact in vitro and in cells via non-overlapping domains and provide evidence consistent with the idea that hSPT16 and SSRP1 change the conformation of CK2 upon binding such that it specifically targets p53 over other substrates. Also, UV irradiation apparently induces the association of the complex, thereby increasing the specificity of CK2 for p53 at the expense of other cellular CK2 substrates and leading to an overall increase in p53 serine 392 phosphorylation.