Immunoblotting of ATM in extracts from lymphocytes of three individuals (1-3). F, extracts from freshly isolated lymphocytes; S, extracts from lymphocytes incubated in the presence of 10% FCS for 3 days; and P, extracts from PHA-stimulated lymphocytes (3 days). A total of 30 μg of protein extract was added to each lane of a 4.5% SDS-PAGE gel and immunoblotting performed with ATM-3BA. Protein loading was monitored by Ponceau S staining. Extracts were also included for an A-T lymphoblastoid cell line (L3) (25 μg) and 4, 10, and 25 μg loading for a control lymphoblastoid cell line (C3ABR).