Effect of incubation time on the amount of ATM in PBMCs. Lymphocytes were freshly prepared (F) and incubated for 1 to 5 days in the presence of serum or PHA. A total of 30 μg of extract was used for all lymphocyte samples and 10 and 25 μg of extract were used for C3ABR, a proliferating EBV-transformed cell line. Immunoblotting was performed using ATM-3BA antibody and protein loading was determined with Ponceau S staining.