W0168

Crystal Structure of the Catalytic Domain of Human DOT1L, a Non-SET Domain Nucleosomal Histone Methyltransferase. Jinrong Min, Qin Feng, Zhizhong Li, Yi Zhang, Rui-ming Xu, Cold Spring Harbor Laboratory, 1 Bungtown Rd., Cold Spring Harbor, NY 11724 USA.

Dot1 is an evolutionarily conserved histone methyltransferase that methylates lysine-79 of histone H3 in the core domain. Unlike other histone methyltransferases, Dot1 does not contain a SET domain, and it specifically methylates nucleosomal histone H3 but not free histones. We have solved a 2.5A resolution structure of the catalytic domain of human Dot1, hDOT1L, complexed with S-adenosyl-L-methionine (SAM). The structure reveals a unique organization of a mainly alpha-helical N-terminal domain and a central open a/b structure. It also reveals an active site consisting of a SAM-binding pocket and a potential lysine-binding channel. Structure guided biochemical analyses show that a flexible, positively charged region at the C-terminus of the catalytic domain is critical for nucleosome binding and enzymatic activity. The structural basis for nucleosome specificity of hDOT1L is revealed from molecular modeling of nucleosome-hDOT1L interactions. These analyses provide mechanistic insights into the catalytic mechanism and nucleosomal specificity of Dot1 proteins.