(A) TdT–Ku interaction in Molt-4 lymphoblasts. Molt-4
lymphoid cell extracts (500 μg) were incubated with mAbs specific for
Ku 70 (N3H10), Ku86 (111), Ku70/86 (162), or TdT (5100) as
indicated above the lanes. Immunoprecipitated complexes were analyzed
as described above. The blot was serially probed with rabbit anti-TdT
(1:500 dilution; Bottom), mouse anti-Ku70 (1:1 dilution;
Middle), or mouse anti-Ku86 antibodies (1:4,000
dilution; Top). The blot had to be exposed for a longer
time to obtain a signal corresponding to Ku86. To prevent overexposure
of other lanes, a separate exposure was obtained and included for lane
5. (B) Effect of EtBr on TdT–Ku interactions. Protein
complexes were immunoprecipitated in the absence (lanes 1–3) or
presence (lanes 4–6) of 100 μg/ml EtBr with anti-TdT,
anti-Ku70/Ku86 heterodimer, and anti-DNA-PKcs mAbs (lanes 1 and
4, 2 and 5, 3 and 6, respectively) from Molt-4 cell extracts, resolved
by SDS/PAGE, and analyzed by Western blotting by using anti-Ku86
as described in A.