Fig. 4. Analysis of material co-eluting with Flag–R2-PPP4c. Flag–R2-PPP4c material eluted with Flag peptide from the anti-Flag agarose column was concentrated and analysed by SDS-PAGE. Proteins bands were detected using Coomassie blue and excised from the gel prior to tryptic digestion and identification by mass spectrometry. The bands at 70 kDa and 40 kDa are believed to be artefacts since they stain more strongly than Flag–R2 and PPP4c and they have also been noted in the eluates with other Flag-tagged proteins. Protein methyltransferase JBP1 is contained within the band at 70 kDa. The other proteins in these bands were not identifiable. The weak protein bands at 50 kDa are - and ß-tubulin.