Abstract

MLL (alias HRX), a SET domain histone methyltransferase involved in epigenetic gene regulation, is cleaved at two sites (12482972; 12393701) by a threonine aspartase termed Taspase1 (14636557). Cleavage is between the conserved Asp-Gly in the motif. The resulting N- and C-terminal fragments (p320 and p180) associate to form a stable heterodimer which localises to the nucleus (12482972). In the absence of Taspase1 (by RNAi), MLL is not cleaved and HOX gene expression becomes deregulated (14636557). It was recently pointed out that the MLL cleavage sites are virtually identical to a conserved cleavage site in the general transcription factor TFIIA (the alfa/beta precursor) (15257296). Although it has not been shown that Taspase1 cleaves TFIIA, the regular expression for this motif takes this possibility into account.