DOT1L Complex Regulates Transcriptional Initiation 1 in Human Cells

DOT1L, the only H3K79 methyltransferase in human cells and a homolog of the yeast Dot1, normally forms a complex with AF10, AF17 and ENL/AF9, is dysregulated in most of the cases of mixed lineage leukemia (MLL) and is believed to regulate transcriptional elongation without much evidence. Here we show that the depletion of DOT1L reduced the global occupancy without affecting the traveling ratio or the elongation rate of Pol II, suggesting it not a major elongation factor. An examination of general transcription factors (GTFs) binding revealed globally reduced TBP and TFIIA occupancies near promoters after DOT1L loss, pointing to a role in transcriptional initiation. Proteomic studies uncovered that DOT1L regulates transcriptional initiation likely by facilitating the recruitment of TFIID. Moreover, ENL, a DOT1L complex subunit with a known role in DOT1L recruitment, also regulates transcriptional initiation. Furthermore, DOT1L stimulates H2B monoubiquitination by limiting the recruitment of human SAGA complex, and the connection between Dot1/DOT1L and SAGA complex is conserved between yeast and human. These results advanced current understanding of roles of DOT1L complex in transcriptional regulation and MLL.