Trithorax group (TrxG) protein that has histone methyltransferase activity (PubMed:13679578, PubMed:16882982). Specifically trimethylates 'Lys-4' of histone H3 (H3K4me3), a specific tag for epigenetic transcriptional activation (PubMed:13679578, PubMed:16882982). TrxG proteins are generally required to maintain the transcriptionally active state of homeotic genes throughout development. Does not act as a coactivator required for transcriptional activation, but specifically prevents inappropriate Polycomb Group (PcG) silencing of homeotic genes in cells in which they must stay transcriptionally active (PubMed:15031712). L-lysyl(4)-[histone H3] + 3 S-adenosyl-L-methionine = 3 H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl(4)-[histone H3] + 3 S-adenosyl-L-homocysteine Component of a large multiprotein complex distinct from complexes containing ash2 or brm (PubMed:9735357). Interacts (via SET domain) with trx (via SET domain) (PubMed:10454589, PubMed:10656681). Interacts with nej/cbp (PubMed:11094082). Localizes at the promoter of active genes. Expressed throughout development but is present at higher levels during the embryonic and pupal stages than during the larval stages. During the larval stages it accumulates primarily in imaginal disks. Expressed both maternally and zygotically. During oogenesis it accumulates in the nurse cells of developing egg chambers. The SET domain is sufficient for methyltransferase activity. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. SET2 subfamily. Was reported to trimethylate H3 'Lys-9' and H4 'Lys-20' (PubMed:12397363). Was also reported to bind non-coding RNAs of trithorax response element (TRE) (PubMed:16497925). However, both papers were retracted because some data, results and conclusions are not reliable. Contaminating sequence. Potential poly-A sequence.