Two domains in C/EBPϵ interact with Rb. (A) NB4 lysates were incubated with either various GST-C/EBPϵ fusion proteins or GST alone as indicated in the figure. Bound Rb was detected by Western blot analysis. NB4 lysate (10% of the input) was used as control for Rb expression. (B) A deduced Rb binding sequence of C/EBPϵ is similar to that of E2F1. The amino acids critical for the E2F1-Rb binding are shown in bold. (C) In vitro–translated C/EBPϵ (input) was incubated with either GST or GST-Rb followed by Western blot analysis with C/EBPϵ antibody.