Histone methyltransferase, which in complex with zfp-1, methylates 'Lys-79' of histone H3 to activate transcription (Probable). During stress, the zfp-1-dot-1.1 complex also plays a role in the deubiquitination of histone H2B sites, which negatively modulates the RNA polymerase II-induced transcription of highly expressed genes (PubMed:23806335). Involved in controlling tissue-specific gene expression, particularly in the epidermis (PubMed:31088904). L-lysyl(79)-[histone H3] + 3 S-adenosyl-L-methionine = 3 H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl(79)-[histone H3] + 3 S-adenosyl-L-homocysteine Interacts with zfp-1 (via C-terminus) to form a heterodimer known as the zfp-1-dot-1.1 complex or DotCom complex. zfp-1 and dot-1.1 colocalize to promoters of highly expressed genes (PubMed:23806335). zfp-1 recruits dot-1.1 (PubMed:23806335). RNAi-mediated knockdown results in the ectopic expression of the neuronal identity-inducing transcription factor che-1 in the epidermis. In contrast to other lysine histone methyltransferases, it does not contain a SET domain, suggesting the existence of another mechanism for methylation of lysine residues of histones. Belongs to the class I-like SAM-binding methyltransferase superfamily. DOT1 family.