Displacement affinity chromatography purification of PP1 complexes from HeLa cell nuclei. (a) A HeLa cell nuclear extract was incubated with microcystin-Sepharose, washed extensively and eluted with the GKKRARA ADLE peptide, followed by GKKRVRW ADLE peptide and finally with 3 M NaSCN. Each fraction was concentrated to an equal volume, run on 4–12% SDS-PAGE (Invitrogen) and stained with Collodial blue. Individual bands were excised, trypsin digested and identified by mass spectrometry (see Additional files 2 and 4). In (b) the same samples from panel (a) were blotted to a membrane and probed with antibodies to proteins identified by mass spectrometry. Protein names are defined in abbreviations list.