3120 Nucleic Acids Research, 2009, Vol. 37, No. 9 Figure 6. CK1d phosphorylates ERa and AIB1 in vitro. (A) Schematic representation of human ERa. AF: activator function. (B) In vitro kinase assays were performed using puriﬁed recombinant human CK1d as source of enzyme and: (i) full-length recombinant human ERa, (ii) GST- recombinant human ERa (aa 1–280) and (iii) GST-recombinant human ERa (aa 283–595), as substrates. (C) Schematic diagram of human AIB1