UASt regulatory sequences drive expression of the full-length Hsap\DOT1L open reading frame (corresponds to GB:NM_032482.3), mutated to carry a p.Lys1025Met change (variant identified in a patient with global developmental delay). The coding sequence is tagged at the C-terminal end with three copies of Tag:HA. The human ORF is flanked by a pair of incompatible FRT sites (FRT5 and FRT2), which allows for future in vivo exchange of either the promoter or tag sequence.