Stability of ATM protein in PBMCs and lymphoblastoid cells. Cells were incubated in cycloheximide (25 μg/mL) for the times indicated before preparation of extracts for separation on SDS-PAGE and immunoblotting with ATM-3BA antibody. A total of 30 μg of protein was loaded for PHA-stimulated cells and for lymphoblastoid cells C3ABR, while 140 μg of protein was used for unstimulated PBMCs. Controls were included as in Fig 1. Exposure times differed among C3ABR, PHA-stimulated cells, and freshly isolated PBMCs.