Treatment of C. trachomatis-infected cells with the protein phosphatase inhibitor okadaic acid (OA) at different concentrations (19) for the last 2 h or for different periods of time during infection led to increased phosphorylation of ATM at Ser1981 (pATM) in a concentration- and exposure time-dependent manner compared to untreated infected cells (Fig. 1C and D). This evidence concerns the gene ATM and infection.