Dot1 binding induces chromatin rearrangements by histone methylation-dependent and -independent mechanisms

Targeting Dot1 did not activate transcription at a euchromatic locus. However, chromatin-bound Dot1 derepressed heterochromatin-mediated gene silencing over a considerable distance. Unexpectedly, Dot1-mediated derepression was established by both a H3K79 methylation-dependent and a methylation-independent mechanism; the latter required the histone acetyltransferase Gcn5. By monitoring the localization of a fluorescently tagged telomere in living cells, we found that the targeting of Dot1, but not its methylation activity, led to the release of a telomere from the repressive environment at the nuclear periphery. This probably contributes to the activity-independent derepression effect of Dot1.Targeting of Dot1 promoted gene expression by antagonizing gene repression through both histone methylation and chromatin relocalization. Our findings show that binding of Dot1 to chromatin can positively affect local gene expression by chromatin rearrangements over a considerable distance.Post-translational modifications of histone proteins are intimately involved in regulation of gene expression [1]. Histone modifications can influence chromatin structure either directly or via proteins that specifically recognize the modified histones [1]. Methylation of histone H3 lysine 79 (H3K79) by Dot1 (also known as KMT4, DOT1L, mDot1 and grappa) is a histone modification that is highly conserved between species [2]. Several studies have linked Dot1 to gene activation. For example, methylated H3K79 is predominantly located in euchromatic regions of the genome [2-8], and Dot1 has been implicated in reactivation of tumor-suppressor genes upon DNA demethylation [9]. Furthermore, in human leukemias bearing chromosomal translocations at the mixed lineage leukemia (MLL) or clathrin assembly lymphoid myeloid (CALM) genes, mistargeting of DOT1L leads to transcript upregulation [10-13]. These leukemia-associated fusion proteins recruit DOT1L to target genes, with a concomitant increase in H3K79