1.3 Histone variants
Histone variants are non-allelic isoforms of core histones that have specialized functions resulting from its distinct amino acid constitution. All histone families except for H4 histone have variant forms (Kamakaka and Biggins, 2005). Unlike core histones, which are only expressed during S phase, histone variants are continuously expressed throughout the cell cycle and incorporated into DNA in a replication-independent manner (Sansoni et al., 2014). A great number of histone variants have been discovered and well studied to date, as illustrated in Table 1.
CenH3 is a ubiquitously expressed variant, which is enriched at the centromeric region. It is essential for chromosome stability and accurate chromosome segregation …show more content…
H2A variants are mostly distinguished from their counterpart by their unique C-terminal and N-terminal tails. MacroH2A is a H2A variant found involved in maintaining X-chromosome inactivation. It localizes to the inactive-X chromosome and inhibits gene activation when it is binding. Studies suggest this is achieved by blocking the access of transcriptional factors and co-activators to DNA through its C-terminal tail (Kamakaka and Biggins, 2015, Perche et al., 2000). Another novel diversification that gives raise to an important group of histone variant, H2A.Z, is found in the acidic patch. The acidic patch is a region on the surface of the nucleosomes which consists of 7 acidic residues (6 from H2A, 1 from H2B). It contacts with the N-terminal tail of histone H4 from the neighboring nucleosome, and is required for nucleosome-nucleosome interaction and high order chromatin condensation (Fan et al., 2004 and Zhou et al., 2007). H2A.Z is a universal variant, that has 3 more acidic residuals, and hence has an extended acidic patch. This allows stronger electrostatic interactions to be generated between the neighboring nucleosomes. As a result, H2A.Z incorporation favors the formation of a higher order chromatin
Histone variants are non-allelic isoforms of core histones that have specialized functions resulting from its distinct amino acid constitution. All histone families except for H4 histone have variant forms (Kamakaka and Biggins, 2005). Unlike core histones, which are only expressed during S phase, histone variants are continuously expressed throughout the cell cycle and incorporated into DNA in a replication-independent manner (Sansoni et al., 2014). A great number of histone variants have been discovered and well studied to date, as illustrated in Table 1.
CenH3 is a ubiquitously expressed variant, which is enriched at the centromeric region. It is essential for chromosome stability and accurate chromosome segregation …show more content…
H2A variants are mostly distinguished from their counterpart by their unique C-terminal and N-terminal tails. MacroH2A is a H2A variant found involved in maintaining X-chromosome inactivation. It localizes to the inactive-X chromosome and inhibits gene activation when it is binding. Studies suggest this is achieved by blocking the access of transcriptional factors and co-activators to DNA through its C-terminal tail (Kamakaka and Biggins, 2015, Perche et al., 2000). Another novel diversification that gives raise to an important group of histone variant, H2A.Z, is found in the acidic patch. The acidic patch is a region on the surface of the nucleosomes which consists of 7 acidic residues (6 from H2A, 1 from H2B). It contacts with the N-terminal tail of histone H4 from the neighboring nucleosome, and is required for nucleosome-nucleosome interaction and high order chromatin condensation (Fan et al., 2004 and Zhou et al., 2007). H2A.Z is a universal variant, that has 3 more acidic residuals, and hence has an extended acidic patch. This allows stronger electrostatic interactions to be generated between the neighboring nucleosomes. As a result, H2A.Z incorporation favors the formation of a higher order chromatin