GO:0140956 histone H3K79 trimethyltransferase activity

Histone H3K79 trimethyltransferase activity (GO:0140956) is a molecular function that catalyzes the addition of three methyl groups to lysine 79 of histone H3, forming H3K79me3. This modification is part of the epigenetic code that regulates chromatin structure and gene expression. The enzyme responsible, DOT1, is unique among histone methyltransferases because it lacks a SET domain and methylates a residue located in the globular core of the histone, rather than the unstructured tail. In kinetoplastids, two DOT1 enzymes cooperate to mediate efficient ubiquitin-independent histone H3 lysine 76 trimethylation, demonstrating evolutionary conservation of this activity. Understanding GO:0140956 is important for researchers studying chromatin dynamics, transcriptional control, and the role of histone modifications in development and disease. The reaction consumes S-adenosyl-L-methionine (SAM) and produces S-adenosyl-L-homocysteine (SAH), linking this activity to cellular metabolism. Because H3K79 methylation is associated with active transcription and DNA damage response, tools to manipulate this activity are valuable for functional genomics.

GO:0140956 is defined as the catalysis of the reaction: L-lysyl79-[histone H3] + 3 S-adenosyl-L-methionine = 3 H+ + N6,N6,N6-trimethyl-L-lysyl79-[histone H3] + 3 S-adenosyl-L-homocysteine. This represents the successive addition of up to three methyl groups to the lysine residue at position 79 of histone H3, producing the trimethylated form H3K79me3. The activity is also known as histone H3K79 trimethylase activity, histone H3-K79 trimethylation, and histone lysine N-trimethyltransferase activity (H3-K79 specific).

GO:0140956 is important because H3K79 trimethylation is a conserved epigenetic mark that influences chromatin accessibility and transcriptional programs. In kinetoplastids, two DOT1 enzymes cooperate to mediate efficient ubiquitin-independent histone H3 lysine 76 trimethylation, highlighting a non-canonical mechanism that may inform studies in other organisms. Dysregulation of H3K79 methylation has been linked to developmental defects and cancer, making this activity a potential therapeutic target. Researchers use CRISPR models to dissect the function of DOT1 enzymes and their role in gene regulation.

The following genes and proteins are directly involved in or regulate histone H3K79 trimethyltransferase activity.

Histone H3K79 trimethyltransferase activity is regulated at multiple levels. In kinetoplastids, two DOT1 enzymes cooperate to mediate efficient ubiquitin-independent histone H3 lysine 76 trimethylation, indicating that enzyme abundance and partnership can control activity. The availability of SAM and the accumulation of SAH can influence methyltransferase activity through metabolic feedback. Additionally, post-translational modifications of DOT1 enzymes and their interacting partners may modulate recruitment to chromatin.

Dysregulation of H3K79 methylation has been implicated in leukemia and other cancers. DOT1L, the enzyme responsible for H3K79 methylation, is a known therapeutic target in MLL-rearranged leukemia. Aberrant H3K79me3 levels can alter gene expression programs that drive oncogenesis.

Proper H3K79 methylation is essential for normal development. In kinetoplastids, two DOT1 enzymes cooperate to mediate efficient ubiquitin-independent histone H3 lysine 76 trimethylation, and disruption of this activity can lead to growth defects. In higher organisms, loss of DOT1L function results in embryonic lethality and developmental abnormalities.

H3K79 methylation is involved in the DNA damage response. The mark recruits proteins such as 53BP1 to sites of DNA damage, and its loss can lead to genome instability. This links GO:0140956 to cancer predisposition and aging.

ChIP with antibodies against H3K79me3 can map the genomic distribution of this mark. This method is used to determine whether DOT1 enzymes are recruited to specific loci.

Mass spectrometry can quantify H3K79 methylation states and identify interacting proteins. It is used to confirm the trimethylation activity of DOT1 enzymes.

Western blotting with H3K79me3-specific antibodies is a standard method to assess enzyme activity after genetic manipulation.

Genome-wide CRISPR screens can identify genes that regulate H3K79 methylation. This approach is used to discover novel regulators of GO:0140956.

Researchers studying histone H3K79 trimethyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in the regulation of H3K79 methylation, chromatin state, and downstream phenotypes. EDITGENE provides a comprehensive suite of CRISPR services to enable such functional studies.

Histone H3K79 trimethyltransferase activity (GO:0140956) is a key epigenetic function that regulates chromatin structure and gene expression. The enzyme DOT1L and its paralogs catalyze the successive methylation of H3K79 using SAM as a cofactor. This activity is conserved across species and is implicated in cancer and developmental disorders. CRISPR-based models are powerful tools to dissect the molecular mechanisms and disease relevance of this modification. EDITGENE offers comprehensive services to support researchers in this field.