Histone Methyltransferases Direct Different Degrees of Methylation to Define Distinct Chromatin Domains

Abstract

The functional significance of mono-, di-, and trimethylation of lysine residues within histone proteins remains unclear. Antibodies developed to selectively recognize each of these methylated states at histone H3 lysine 9 (H3 Lys9) demonstrated that mono- and dimethylation localized specifically to silent domains within euchromatin. In contrast, trimethylated H3 Lys9 was enriched at pericentric heterochromatin. Enzymes known to methylate H3 Lys9 displayed remarkably different enzymatic properties in vivo. G9a was responsible for all detectable H3 Lys9 dimethylation and a significant amount of monomethylation within silent euchromatin. In contrast, Suv39h1 and Suv39h2 directed H3 Lys9 trimethylation specifically at pericentric heterochromatin. Thus, different methylated states of H3 Lys9 are directed by specific histone methyltransferases to "mark" distinct domains of silent chromatin.

Histone H4 lysine 20 monomethylation promotes transcriptional repression by L3MBTL1

“…Histone lysine methylation is coupled with both transcriptional competence (H3K4me3, H3K36me3 and H3K79me2) and silencing (H3K9me3, H3K27me3). Furthermore, the methylation status (mono-, di-or tri-(me1/me2/ me3)) of specific lysines, extends the options for signaling to chromatin (Peters et al, 2003;Rice et al, 2003) as exemplified for H4K20 methylation. H4K20me1 is associated with facultative heterochromatin (Fang et al, 2002;Martens et al, 2005;Sims et al, 2006), and the inactive X chromosome (Kohlmaier et al, 2004).…”

Development of rabbit monoclonal and polyclonal antibodies for detection of site-specific histone modifications and their application in analyzing overall modification levels

“…The level of a site-specific histone modification of any organ can be an indicator for the level in the whole organism. However, this observation clearly does not rule out potential differences among localized and specific regions of a chromosome during the development of an organism [2,17,18].…”

“…Both the H3K27Me2 and H3K9Me2 shared an "AR[Me2 K]S" amino acid motif, which might be part of the epitope peptide has an amino acid motif "ART[Me2K]", similar but not identical to that of H3K9Me2 peptide, which could explain its weak inhibition effect. Since histone H3K9 shares a similar flanking amino acid sequence to H3K4 and K27, it is a possibility that the antibodies can crossreact to H3K4 and K27 [17]. A lot of antibodies commercially available for H3K9Me2 also seemed to have more or less some degree of crossreactivity, including widely used antibodies from Upstate Company (for example, product #05-768).…”

“…A lot of antibodies commercially available for H3K9Me2 also seemed to have more or less some degree of crossreactivity, including widely used antibodies from Upstate Company (for example, product #05-768). Using a different immunization strategy such as immunizing with two-branched peptides, it was claimed that the resulting antibodies (Upstate #07-441) for H3K9Me2 had minimal crossreaction with H3K4Me2 or H3K27Me2 [17,18]. However, this strategy of not immunizing with original amino-acid sequences might produce antibodies that crossreact with other structural features in the organism or variant histone proteins.…”

Structural dynamics of protein lysine methylation and demethylation

“…To further test the hypothesis that a single residue in the active site of SET-containing HKMTs, which aligns to F281 in DIM-5, is a major determinant of product specificity, F1205 was replaced with tyrosine (F1205Y) in human G9a, a predominant mammalian H3 Lys-9 HKMT that directs euchromatic mono-and dimethylation [52][53][54] but can generate trimethyl-H3K9 in some situations [55]. The mutation did not affect the catalytic activity of G9a; however, the reaction by F1205Y stalled at the monomethyl stage [56].…”