FIG 3.

HPV-18 E6 is phosphorylated by the DNA damage response kinase Chk1. (A) Consensus phosphorylation motifs recognized by ATR, ATM, Chk1, and Chk2 compared with the sequence of the carboxy terminus of HPV-18 E6. *, carboxy terminus of E6; green text, serine/threonine phospho-acceptor. (B) In vitro phosphorylation assay using purified GST fusion proteins of wild-type HPV-18 E6 and the HPV-18 E6 T156E mutant incubated with Chk1 or Chk2 in the presence of [γ-³²P]ATP. (Top) Autoradiograms. (Bottom) Coomassie-stained SDS-PAGE gels. The arrows indicate phospho-E6, the GST E6 fusion protein, the GST control, and the autophosphorylated Chk1 and Chk2.