FIG. 5.

Serine 20 in TRF2 can be phosphorylated by Chk2 in vitro. (A) Candidate Chk2 phosphorylation sites in TRF2 (S20), EBNA1 (S350), and histone H3 (T11) are aligned with the known consensus sites for Chk2 phosphorylation. (B) GST, GST-TRF2(1-90), GST-TRF2(1-90)(S20A), and GST-TRF2(1-90)(S20E) were purified from E. coli cells and visualized by Coomassie blue staining after SDS-PAGE. (C) The purified Chk2 protein at 0 nM, 50 nM (+), or 250 nM (++) was assayed for its ability to phosphorylate GST, GST-TRF2(1-90), GST-TRF2(1-90)(S20A), and GST-TRF2(1-90)(S20E), as indicated. The arrows indicate TRF2(1-90), and the arrowhead indicates a GST-TRF2 breakdown product. Chk2 autophosphorylation is indicated in the upper panel.