Neck and motor domain of MCAK binds to the kinase domain of PLK1. A and B, GST-PLK1 on glutathione beads was incubated with lysates of 293T cells expressing GFP-MCAK or GFP-MCAK deletion mutants, followed by Western blotting with an anti-GFP antibody. C, GST-PLK1, but not GST, interacts with MBP-MCAK(182–586). GST-PLK1 on glutathione beads was incubated with recombinant MBP-MCAK(182–586) purified from E. coli, followed by Western blot analysis with an anti-maltose-binding protein (MBP) antibody. CB, Coomassie Brilliant Blue. D, schematic representation and summary of the binding studies for a series of MCAK deletion mutants assayed in A–C. +, positive; +/−, weak positive; −, negative. Numbers indicate positions of the amino acid residues. E, schematic illustration of PLK1 functional domain and deletion mutants used in F. Numbers indicate the positions of the amino acid residues. F, GST-PLK1 deletion mutants interact with MCAK-His. GST fusion proteins containing N- and C-terminal PLK bound to glutathione beads were incubated with recombinant MCAK-His purified from Sf9 cells followed by Western blot analysis with an anti-His antibody.