The MLL complex is a histone methyltransferase complex that plays a key role in transcriptional activation by covalently modifying the nucleosome. However, our knowledge of its structure and mechanism is limited. We hypothesize that the MLL complex has a precise binding interaction with the nucleosome that can be determined via X-ray crystallography. Solving the structure of this complex bound to its nucleosome substrate will inform us of its mechanism of chromatin regulation.