TdT ubiquitylation <i>in vivo</i> or <i>in vitro</i>.

<p>(A) Endogenous TdT ubiquitylation in Jurkat cells. Immunoprecipitation was carried out using an anti-TdT antibody (lanes 4 and 6) or rabbit pre-immune serum (pre-IS) (lanes 3 and 5). Immunoprecipitants were subjected to SDS-PAGE and immunoblotted with anti-Ub (FK2) or anti-TdT antibody. One mg of whole cell lysate was used for each immunoprecipitation. (B) <i>In vitro</i> TdT ubiquitylation. The substrate His-TdT was incubated under ubiquitylation conditions with purified proteins. His-TdT and His-BPOZ-2 were purified from <i>E. coli</i> and the Flag-tagged proteins were purified from 293 T cells. To obtain Cul3/Rbx1 or BPOZ-2/Cul3/Rbx1 complexes, 293 T cells were co-transfected with the circled plasmids (lanes 10 and 11). After electrophoresis with a denaturing 7.5% polyacrylamide gel, ubiquitylated TdT was detected using an anti-TdT antibody. (C and D) Kinetics of TdT ubiquitylation in the absence (C) or presence (D) of the BPOZ-2/Cul3/Rbx1 complex. The incubation time after the addition of His-TdT is given above. The reaction products were separated by 7.5% SDS-PAGE and immunoblots were probed with anti-TdT antibody or anti-Flag antibody. The ratio of ubiquitylated His-TdT to unmodified His-TdT was determined with ImageJ. The band density for ubiquitylated His-TdT was defined as 100%.