The H3 -binding domain (H3BD) resides within the C-terminal regions of MTA proteins. A. The binding of various MTA1 deletion mutants to H3 tail peptide in vitro. The left panel illustrates the primary structures of MTA1 and various mutants. Also indicated are four structural motifs in the N-terminal regions of MTA proteins, namely BAH, ELM2, SANT and ZnF and the C-terminal H3BD determined here. The proteins were synthesized and 35S-met labeled and subjected to in vitro pulldown assay with and without the immobilized H3 peptide. B. The C-terminal region of MTA1 exhibits the same H3 peptide-binding specificity as the full-length MTA1. The experiment was performed as in B except additional immobilized H3 peptides were included. C. The recombinant MTA1 and MTA2 C-terminal regions are sufficient for binding H3 tail peptide. The 6xHis-tagged MTA1(454–715) and 6xHis-MTA2(427–668) were expressed and purified from E.coli and subjected to in vitro pulldown assay with immobilized H3 tail peptide. D. The H3-binding activity is also mapped to the C-terminal region of MTA2. The MTA2 and its N- and C- terminal regions were expressed as 35S-Met labeled proteins and subjected to in vitro pulldown assay with immobilized H3 tail peptide.