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Post-translational modifications of histones H3 and H4 associated with the histone methyltransferases Suv39h1 and G9a

DOI: 10.1186/gb-2007-8-12-r270

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Abstract:

The amino-terminal tails of nucleosomal histones protrude from the DNA and are subject to covalent modifications. These modifications include lysine acetylation, lysine and arginine methylation, serine and threonine phosphorylation, ADP-ribosylation, and ubiquitination [1]. Histone lysine methylation can have different effects depending on the residue that is modified: methylation of histone H3 at Lys4 (H3K4) is associated with gene activation, whereas methylation of H3K9, H3K27, and H4K20 generally correlates with transcriptional repression [2-4]. The roles of H3K36 and H3K79 methylation remain elusive; indeed, these modifications are associated with both transcriptional activation and repression [5,6].Lysine residues can be mono-, di-, or trimethylated, inducing different biological responses [3,7,8]. Thus, for example, highly condensed heterochromatic regions show a high degree of trimethylated H3K9 (H3K9me3), whereas euchromatic regions are preferentially enriched in mono- and dimethylated H3K9 [2,3]. Histone lysine methylation is mediated by histone methyltransferases (HMTs), many of which contain a conserved SET [Su(var)3-9, Enhancer-of-zeste, Trithorax] domain, such as Suv39h1 (Suppressor of variegation 39h1) and G9a [1,2,9]. Suv39h1 belongs to a family of peri-centromeric proteins and is responsible for H3K9 trimethylation [10-13]. G9a (EuHMTase-2) is the major methylase responsible for mono- and dimethylation of H3K9 in euchromatic regions [14,15], but it may also be present in heterochomatic regions [16].Covalent modifications of histones can regulate gene expression directly or through recruitment of non-histone effector proteins [2,17]. These effector proteins bind modified chromatin using a variety of chromatin-binding domains. For example, bromodomains recognize acetylated lysines, whereas chromo, MBT, Tudor, W40 domains and PHD fingers, recognize methylated lysines [17,18]. Repressive methyl-lysine modifications are recognized by chromodomain-containi

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