Figure 5. Analysis of p53 phosphorylation and total protein levels shows p53 phosphorylation at serine15 precedes accumulation of total p53 protein. (A) GM0536 lymphoblastoid cells were treated with 8 Gray of gamma irradiation and p53 phosphorylation at serine15 and total p53 protein levels were monitored over time following irradiation and compared on a per-cell basis. (B) Quantitation of the change in median fluorescence of the population over time showed rapid induction of phosphorylation in the first hour followed by a more gradual accumulation of total p53 protein. Similar analyses can be performed on cancerous cells to determine p53 status and activation.