Association of mitotic PP1 isoforms with Rb or Rb-deletion mutants. The GST-Rb fusion proteins, full-length (Rb) and big pocket (RbBP), or the pMAL-Rb fusion proteins, RbBP and carboxyl terminus (RbCT; also indicated in the lower part of the figure), were bound to the appropriated beads and used to co-precipitate (GST PD or pMAL PD) the PP1 isoforms from mitotic Hela cells lysate (2.5 mg/PD). This was followed by electrophoresis, to which cell lysate was also added (Lys), and immunoblotting to detect the PP1 isoforms (PP1α, γ1 and δ blot) and the GST- or pMAL-fusion proteins (GST blot or pMAL blot). Detection of the unrelated FAK protein (FAK blot) in the cell lysates used for the GST or pMAL PD assays confirmed the use of equal protein amounts. The data presented are representative of multiple experiments.