BioProject

Heterochromatic histone H3 methylation at lysine 9 (H3K9me2/3) and lysine 27 (H3K27me3) is generally catalyzed by SUV39 and EZH family methyltransferases, respectively, and has distinct functions in most eukaryotes. More...

Heterochromatic histone H3 methylation at lysine 9 (H3K9me2/3) and lysine 27 (H3K27me3) is generally catalyzed by SUV39 and EZH family methyltransferases, respectively, and has distinct functions in most eukaryotes. In contrast, the ciliated protozoan Tetrahymena lacks the SUV39 enzyme, and the EZH enzyme Ezl1p is responsible for the deposition of both H3K9me3 and H3K27me3 during Piwi-directed DNA elimination. Understanding how both modifications are catalyzed by the EZH enzyme should shed light on the mechanism and the evolution of the division of labor between the two heterochromatic histone methyltransferase families in eukaryotes. Here, we show that loss of the novel protein Ded2p abolishes the accumulation of H3K9me3 but not H3K27me3 in Tetrahymena. The phenotypes of DED2 KO cells revealed that H3K27me3 is sufficient for promoting secondary small RNA biogenesis but not for suppressing TEs, assembling heterochromatin bodies and completing DNA elimination. Ded2p associates with Ezl1p through Rnf2p, a component of Tetrahymena Polycomb Repressive Complex 2 (PRC2) to promote the accumulation of H3K9me3. Our results indicate that there are functional distinctions between H3K9me3 and H3K27me3 in different steps of the DNA elimination process and the specificity of the methyltransferase activity of PRC2 can be modulated by its associated factor to catalyze H3K9me3. Overall design: The primery biogenesis, homology-dependent degradation, and heterochromatin dependent secondary biogenesis of ~29-nt small RNA (scnRNA) were analyzed by sequencing 16-32-nt small RNAs at 3, 6 and 10 hours post-mixing of DED2 KO Tetrahymena thermophila strains Less...