CDK9 Phosphorylates p53 on Serine Residues 33, 315 and 392

Tumor suppressor p53 is often activated in response to DNA damage or otherforms of stress, leading to either cell cycle arrest or apoptosis. Stress-induced kinasesphosphorylate p53 thereby enhancing its stability, leading to an increase intransactivation of its target genes. Several different protein kinases phosphorylate p53 onmultiple amino acid residues. Here, we report for the first time that Cyclin dependentkinase 9, whose well-known substrate is RNA polymerase II, can also phosphorylate p53.Specifically, Ser33 on the N-terminus and, Ser315 and Ser392 on the C-terminus of p53were found to be phosphorylated. The precise biological role of this phosphorylationremains to be elucidated.