Give a final protein concentration of 0.4 mg/ml. Removal of the denaturant and refolding of the p300 TAZ2 was achieved by dialysis G007-LK web against a buffer containing 20 mM Tris, 100 mM NaCl, 200 mM ZnSO4 and 20 mM DTT, pH 8.5. The refolded TAZ2 then underwent a second dialysis against a buffer containing 20 mM Tris, 100 mM NaCl, 100 mM ZnSO4 and 2 mM DTT, pH 7.5 prior to being loaded onto a cation exchange column. The purified TAZ2 was eluted in 20 mM Tris, 1 M NaCl, 50 mM ZnSO4 and 2 mM DTT, pH 7.5 buffer and then purified to homogeneity by gel filtration chromatography on a Superdex 75 prep-grade column (Amersham Pharmacia) preequilibrated with buffer containing 20 mM Tris, 100 mM NaCl, 20 mM ZnSO4 and 5 mM DTT, pH 7.5. The purified TAZ2 was shown to be .95 pure by SDSPAGE.Expression and Purification of the B-Myb TADGST-tagged mouse B-Myb TAD (residues 275?76) was expressed as a soluble fusion protein in E. coli and initially purified using glutathione agarose affinity chromatography [33]. B-Myb TAD was obtained after PreScission Protease (Amersham Pharmacia) cleavage of the GST-tag [34], [35]. Briefly, protein samples containing GST-tagged B-Myb TAD were dialysed against PreScission Protease cleavage buffer (50 mM Tris-HCl, 150 mM NaCl, 1 mM EDTA, 1 mM DTT, pH 7.0), prior to addition of PreScission Protease (10 U per mg of protein) and incubation for 16?0 hours at 4uC. The released GST and the GST-tagged PreScission protease were then removed by a second glutathione agarose affinity step, with the B-Myb TAD collected in the flow-through fractions. Homogenous B-Myb TAD was obtained after gel filtration chromatography on a Superdex 75 prep-grade column (Amersham Pharmacia), preequilibrated with buffer containing 20 mM Tris, 100 mM NaCl, 20 mM ZnSO4 and 5 mM DTT, pH 7.5. Purified B-Myb TAD was shown to be .95 pure by SDS-PAGE.Circular Dichroism SpectroscopyCD data were acquired on a JASCO 715 spectropolarimeter at 25uC from protein samples of 8 to 20 mM in a 0.1 cm pathlength cell. Typically, spectra were recorded from 190 to 250 nm at a scan speed of 20 nm per minute, with each spectrum representing the average of 10 accumulations. Samples of p300 TAZ2 were prepared in a buffer containing 20 mM Tris, 100 mM NaCl, 2 mM DTT and 20 mM ZnSO4, pH 7.5, whilst samples of the BMyb TAD were in a 25 mM sodium phosphate, 100 mM NaCl buffer at pH 7.0. Prior to secondary structure analysis, CD spectra were corrected for buffer absorbance and the raw data converted to molar CD per residue.Fluorescence Emission SpectroscopyFigure 1. Schematic representations of the organisation of the functional regions and domains of human B-Myb and p300. Panel A shows the positions of functional domains in the transcriptional coactivator p300, as well as a partial list of proteins that bind to the CH3/E1A-binding region. Panel B illustrates the tripartite functional organisation of the B-Myb protein, which contains an N-terminal DNA binding Ganetespib web region (DBD) formed by three highly homologous domains (R1, R2 and R3), a central transactivation domain (TAD), and towards 11967625 the Cterminus a highly conserved region (CR) and negative regulatory domain (NRD). doi:10.1371/journal.pone.0052906.gIntrinsic tryptophan fluorescence spectra were acquired on a Perkin Elmer LS50B luminescence spectrometer using a 1 cm path length cuvette, essentially as described previously [31]. For the B-Myb TAD, spectra were recorded from 3 mM samples in a 25 mM sodium phosphate, 100 mM NaCl buffer at pH 7.0.Give a final protein concentration of 0.4 mg/ml. Removal of the denaturant and refolding of the p300 TAZ2 was achieved by dialysis against a buffer containing 20 mM Tris, 100 mM NaCl, 200 mM ZnSO4 and 20 mM DTT, pH 8.5. The refolded TAZ2 then underwent a second dialysis against a buffer containing 20 mM Tris, 100 mM NaCl, 100 mM ZnSO4 and 2 mM DTT, pH 7.5 prior to being loaded onto a cation exchange column. The purified TAZ2 was eluted in 20 mM Tris, 1 M NaCl, 50 mM ZnSO4 and 2 mM DTT, pH 7.5 buffer and then purified to homogeneity by gel filtration chromatography on a Superdex 75 prep-grade column (Amersham Pharmacia) preequilibrated with buffer containing 20 mM Tris, 100 mM NaCl, 20 mM ZnSO4 and 5 mM DTT, pH 7.5. The purified TAZ2 was shown to be .95 pure by SDSPAGE.Expression and Purification of the B-Myb TADGST-tagged mouse B-Myb TAD (residues 275?76) was expressed as a soluble fusion protein in E. coli and initially purified using glutathione agarose affinity chromatography [33]. B-Myb TAD was obtained after PreScission Protease (Amersham Pharmacia) cleavage of the GST-tag [34], [35]. Briefly, protein samples containing GST-tagged B-Myb TAD were dialysed against PreScission Protease cleavage buffer (50 mM Tris-HCl, 150 mM NaCl, 1 mM EDTA, 1 mM DTT, pH 7.0), prior to addition of PreScission Protease (10 U per mg of protein) and incubation for 16?0 hours at 4uC. The released GST and the GST-tagged PreScission protease were then removed by a second glutathione agarose affinity step, with the B-Myb TAD collected in the flow-through fractions. Homogenous B-Myb TAD was obtained after gel filtration chromatography on a Superdex 75 prep-grade column (Amersham Pharmacia), preequilibrated with buffer containing 20 mM Tris, 100 mM NaCl, 20 mM ZnSO4 and 5 mM DTT, pH 7.5. Purified B-Myb TAD was shown to be .95 pure by SDS-PAGE.Circular Dichroism SpectroscopyCD data were acquired on a JASCO 715 spectropolarimeter at 25uC from protein samples of 8 to 20 mM in a 0.1 cm pathlength cell. Typically, spectra were recorded from 190 to 250 nm at a scan speed of 20 nm per minute, with each spectrum representing the average of 10 accumulations. Samples of p300 TAZ2 were prepared in a buffer containing 20 mM Tris, 100 mM NaCl, 2 mM DTT and 20 mM ZnSO4, pH 7.5, whilst samples of the BMyb TAD were in a 25 mM sodium phosphate, 100 mM NaCl buffer at pH 7.0. Prior to secondary structure analysis, CD spectra were corrected for buffer absorbance and the raw data converted to molar CD per residue.Fluorescence Emission SpectroscopyFigure 1. Schematic representations of the organisation of the functional regions and domains of human B-Myb and p300. Panel A shows the positions of functional domains in the transcriptional coactivator p300, as well as a partial list of proteins that bind to the CH3/E1A-binding region. Panel B illustrates the tripartite functional organisation of the B-Myb protein, which contains an N-terminal DNA binding region (DBD) formed by three highly homologous domains (R1, R2 and R3), a central transactivation domain (TAD), and towards 11967625 the Cterminus a highly conserved region (CR) and negative regulatory domain (NRD). doi:10.1371/journal.pone.0052906.gIntrinsic tryptophan fluorescence spectra were acquired on a Perkin Elmer LS50B luminescence spectrometer using a 1 cm path length cuvette, essentially as described previously [31]. For the B-Myb TAD, spectra were recorded from 3 mM samples in a 25 mM sodium phosphate, 100 mM NaCl buffer at pH 7.0.
