The active sites of KsgA and sc-mtTFB. A. Close up of the active sites. Residues in sc-mtTFB prior to residue 20 have been truncated, in order to start at a position analogous to the beginning of the KsgA crystal structure. KsgA is shown in blue, with residues mentioned in the text highlighted in yellow. sc-mtTFB is shown in green, with residues highlighted in red. SAM was modeled into the KsgA active site by using the co-crystal structure of ErmC' in complex with SAM (1QAO) as a guide. Similarly, adenosine was modeled into the active site using the co-crystal structure of the DNA methyltransferase M. TaqI in complex with target DNA as a guide . B. Surface representation of the KsgA active site. C. Surface representation of the sc-mtTFB active site.