Induction of the G
checkpoint control by chromatin peptides. A: Expression of cyclin B1 at 12 and 24 hours of peptide fraction treatment. (black bars) control cells; (grey bars) treated cells. The analyses were performed by flow cytometry as described in Materials and Methods. B: Cdc2-cyclin B1 activity determined by ELISA in nuclear extracts obtained from G2 cells. C: Western Blot analysis performed in nuclear extracts obtained from G2 cells. a: inactive phospho-Tyr15 cdc2-cyclin B1 complex; b: active phospho-Ser345 chk1. D: densitometric analysis of the immunoblotting. The values are expressed as percentage of the control. c: control cells; t: treated cells.