p53 Binds to Peptides that Mimic the Phosphorylated Pol II CTD.

<p>Biotinylated CTD peptides bearing four heptad repeats (28-mers) that were unphosphorylated (CTD), Ser5-phosphorylated (Ser5-P-CTD), or Ser2-phosphorylated (Ser2-P-CTD), were adsorbed to streptavidin-coated magnetic beads. Recombinant HA-p53, bearing an HA tag on its N-terminus, was incubated with beads alone or beads bearing peptides. Bound proteins (B) and those remaining in the supernatant (S) were subjected to SDS-PAGE and the presence of p53 was detected using the 1801 mAb. (B) Graphical summary of peptide-bound p53 relative to unbound p53. Depicted are means ± S.E.M. (N = 4). A two-sample <i>t</i>-test (two-tailed, equal variance) comparing p53 binding to the Ser5-phosphorylated CTD peptide <i>vs.</i> the unphosphorylated CTD peptide results in a <i>P</i> value of 0.058. A corresponding analysis of p53 binding to the Ser2-phosphorylated CTD peptide results in a <i>P</i> value of 0.11.