Dynamic Control of the Dot1L Histone Methyltranferase Reveals Precise Kinetics of H3k79me Is Governed By Nucleosome Turnover

Cellular fate is hierarchically controlled by the underlying genetic code, DNA methylation, and histone modifications, which when disrupted can lead to cancer. Fusions of the MLL protein with members of the H3K79-placing complex (DOT1L) result in >80% of MLL-rearranged leukemias. However, despite the discovery of several potent chemical probes for the DOT1L methytransferase, the mechanisms of H3K79-mediated genetic regulation remain poorly understood. Through temporal control of covalent histone mark placement, the unknown mechanisms governing the regulation of the Histone 3, lysine 79 methylation mark (H3k79me) and it’s role in transcriptional elongation are explored. Utilizing chemical induced proximity of the DOT1L H3k79 histone methyltransferase, we selectively recruit the DOT-complex to H3K79me-deficient genes to observe the kinetics of mono, di, and tri H3K79 methylation utilizing time-dependent chromatin immunoprecipitation. In the first example employing chemical-induced-proximity to measure the direct kinetics of histone mark methylation state, we observe that the kinetics of H3K79 is genome-context specific. Further, utilizing Monte Carlo simulations coupling systems of kinetic equations with a physical propogation and exchange, we observe that the kinetics of H3k79me are likely governed by rates of nucleosome turnover rather than active demethylation, which is an active area of debate.