Abstract
BackgroundMethylation of histone H3 lysine 79 (H3K79) by Dot1 is highly conserved among species and has been associated with both gene repression and activation. To eliminate indirect effects and examine the direct consequences of Dot1 binding and H3K79 methylation, we investigated the effects of targeting Dot1 to different positions in the yeast genome.ResultsTargeting 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.ConclusionsTargeting 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.
Highlights
Methylation of histone H3 lysine 79 (H3K79) by Dot1 is highly conserved among species and has been associated with both gene repression and activation
Dot1 is a derepressor The effect of local Dot1 binding and activity on gene expression was investigated by fusing Saccharomyces cerevisiae Dot1 to the Escherichia coli LexA protein and targeting it to LexA operators (LexO), which were engineered into euchromatic and heterochromatic regions of the yeast genome (Figure 1A)
To examine whether Dot1 can block the spread of heterochromatin as a barrier, a LexA-Dot1 fusion protein was expressed in a strain with LexA operators in between a URA3 reporter and the telomeric repeats (Figure 1A)
Summary
Methylation of histone H3 lysine 79 (H3K79) by Dot is highly conserved among species and has been associated with both gene repression and activation. To eliminate indirect effects and examine the direct consequences of Dot binding and H3K79 methylation, we investigated the effects of targeting Dot to different positions in the yeast genome. Methylation of histone H3 lysine 79 (H3K79) by Dot ( known as KMT4, DOT1L, mDot and grappa) is a histone modification that is highly conserved between species [2]. Methylated H3K79 is predominantly located in euchromatic regions of the genome [2,3,4,5,6,7,8], and Dot has been implicated in reactivation of tumor-suppressor genes upon DNA demethylation [9].
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