Nt structural changes are observed in the MEF2 dimers upon binding to TAZ2. One of the MEF2 dimers (shown in blue in figure S3) binds to the same MedChemExpress UKI 1 surface of TAZ2 as both the STAT1 and B-Myb TADs, and would almost certainly compete with these two TADs for binding to TAZ2. A second MEF2 dimer (shown in green) sits adjacent to the STAT1 and B-Myb TAD binding site, whilst the third dimer binds to a distinct surface of TAZ2. The presence of these additional interaction sites would probably allow TAZ2 to simultaneously interact with both MEF2 and B-Myb TAD. The work reported here provides compelling evidence that BMyb TAD binds to a specific region on the surface of the TAZ2 domain of p300, which strongly supports the assignment of p300 as a key POR 8 functional partner of B-Myb in vivo. The two domains bind with moderate affinity, which probably reflects the coupled binding and folding of the B-Myb TAD, but clearly favours the formation of a dynamic complex, well suited to producing a transient activation of gene expression.Supporting InformationFigure S1 Multiple sequence alignment of the highly homologous TADs of mouse (mB-Myb), human (hBMyb), chicken (cB-Myb) and zebrafish B-Myb (zB-Myb). Residues with absolutely conserved sequence identity are highlighted in red, whilst those with conserved sequence similarity in three or more species are highlighted in yellow. The positions of the two potential helices are indicated above the sequence. The consensus sequence is shown below. Amino acids with absolutely conserved sequence identity are shown in uppercase; those with sequence similarity in over 75 of the sequences are shown in lowercase. Similar residues were grouped as follows: AVILM, FYW, KRH, DE, STNQ, PG and C. The symbol `!’ is used to denote either I or V, ` ‘ denotes L or M, ` ‘ denotes F or Y, and `#’ denotes any of NDQE. The alignment was prepared using ClustalW and 16574785 ESPript.cgi (http://npsa-pbil.ibcp.fr/cgi-bin/ align_clustalw.pl). (TIFF) Figure S2 Location of the B-Myb TAD binding site on p300 TAZ2. Panel A shows a ribbon representation of the TAZ2 domain of CBP [30], while panel B shows a contact surface view in the same orientation. In panel C the surface view of CBP TAZ2 has been rotated by 180u about the y axis to reveal the opposite face of the domain. The contact surfaces have been coloured according to the magnitude of the minimal shifts induced in backbone amide resonances of equivalent residues in p300 TAZ2 by binding of the B-Myb TAD. Residues that showed a minimal shift change of less than 0.075 ppm are shown in white, over 0.15 ppm in red, and between 0.075 and 0.15 ppm are coloured according to the level of the shift on a linear gradient between white and red. No chemical shift perturbation data could be obtained for the residues shown in yellow. Panels D-F show the equivalent views of the structure of p300 TAZ2 [67]. The contact surface of p300 TAZ2 is coloured as explained for CBP TAZ2. In addition, the C-terminal 22 residues of the p300 TAZ2 (1813?1834) structure, which are absent from both our p300 TAZ2 construct and the CBP TAZ2 structure (panels A-C) are shown in green. (TIF)Features of the B-Myb TAD-p300 TAZ2 ComplexFigure S3 Comparison of the B-Myb TAD and the DNAbound MEF2 binding sites on p300 TAZ2. Panel A shows a contact surface view of CBP TAZ2 (left) with the location of the BMyb TAD binding site on p300 TAZ2 highlighted as described in figure 5. For comparison, the structure of p300 TAZ2 bound to three MEF2.Nt structural changes are observed in the MEF2 dimers upon binding to TAZ2. One of the MEF2 dimers (shown in blue in figure S3) binds to the same surface of TAZ2 as both the STAT1 and B-Myb TADs, and would almost certainly compete with these two TADs for binding to TAZ2. A second MEF2 dimer (shown in green) sits adjacent to the STAT1 and B-Myb TAD binding site, whilst the third dimer binds to a distinct surface of TAZ2. The presence of these additional interaction sites would probably allow TAZ2 to simultaneously interact with both MEF2 and B-Myb TAD. The work reported here provides compelling evidence that BMyb TAD binds to a specific region on the surface of the TAZ2 domain of p300, which strongly supports the assignment of p300 as a key functional partner of B-Myb in vivo. The two domains bind with moderate affinity, which probably reflects the coupled binding and folding of the B-Myb TAD, but clearly favours the formation of a dynamic complex, well suited to producing a transient activation of gene expression.Supporting InformationFigure S1 Multiple sequence alignment of the highly homologous TADs of mouse (mB-Myb), human (hBMyb), chicken (cB-Myb) and zebrafish B-Myb (zB-Myb). Residues with absolutely conserved sequence identity are highlighted in red, whilst those with conserved sequence similarity in three or more species are highlighted in yellow. The positions of the two potential helices are indicated above the sequence. The consensus sequence is shown below. Amino acids with absolutely conserved sequence identity are shown in uppercase; those with sequence similarity in over 75 of the sequences are shown in lowercase. Similar residues were grouped as follows: AVILM, FYW, KRH, DE, STNQ, PG and C. The symbol `!’ is used to denote either I or V, ` ‘ denotes L or M, ` ‘ denotes F or Y, and `#’ denotes any of NDQE. The alignment was prepared using ClustalW and 16574785 ESPript.cgi (http://npsa-pbil.ibcp.fr/cgi-bin/ align_clustalw.pl). (TIFF) Figure S2 Location of the B-Myb TAD binding site on p300 TAZ2. Panel A shows a ribbon representation of the TAZ2 domain of CBP [30], while panel B shows a contact surface view in the same orientation. In panel C the surface view of CBP TAZ2 has been rotated by 180u about the y axis to reveal the opposite face of the domain. The contact surfaces have been coloured according to the magnitude of the minimal shifts induced in backbone amide resonances of equivalent residues in p300 TAZ2 by binding of the B-Myb TAD. Residues that showed a minimal shift change of less than 0.075 ppm are shown in white, over 0.15 ppm in red, and between 0.075 and 0.15 ppm are coloured according to the level of the shift on a linear gradient between white and red. No chemical shift perturbation data could be obtained for the residues shown in yellow. Panels D-F show the equivalent views of the structure of p300 TAZ2 [67]. The contact surface of p300 TAZ2 is coloured as explained for CBP TAZ2. In addition, the C-terminal 22 residues of the p300 TAZ2 (1813?1834) structure, which are absent from both our p300 TAZ2 construct and the CBP TAZ2 structure (panels A-C) are shown in green. (TIF)Features of the B-Myb TAD-p300 TAZ2 ComplexFigure S3 Comparison of the B-Myb TAD and the DNAbound MEF2 binding sites on p300 TAZ2. Panel A shows a contact surface view of CBP TAZ2 (left) with the location of the BMyb TAD binding site on p300 TAZ2 highlighted as described in figure 5. For comparison, the structure of p300 TAZ2 bound to three MEF2.