Figure 6.

(A) Hyperphosphorylation of coilin reduces coilin self-interaction. GFP-coilin was transfected into HeLa and cells were treated with nocodazole to enrich for mitotic cells (Mit.) or left untreated for interphase cells (Int.). Extracts were subjected to immunoprecipitation with anti-GFP antibodies, followed by SDS-PAGE and western blotting with antibodies against coilin. Equivalent amounts of protein were used for each reaction. (B) Coilin was phosphorylated by casein kinase 2 in vitro. Reactions were conducted as described in the MATERIALS AND METHODS section. Phosphorylation of coilin was dependent on the presence of casein kinase 2 (CKII). Radiolabeled bands present in lane 1 and below the coilin radioactive band in lane 3 are most likely CKII autophosphorylation products.