- Histone-Modifying Enzymes
The packaging of the
eukaryotic genomeinto highly condensed chromatinmakes it inaccessible to the factors required for gene transcription, DNA replication, recombinationand repair. Eukaryoteshave developed intricate mechanisms to overcome this repressive barrier imposed by the chromatin. It is composed of an octamer of the four core histones (H3, H4, H2A, H2B) around which 147 base pairs of DNA are wrapped. Several distinct classes of enzymecan modify histones at multiple sites [Kouzarides T. Cell. (2007) Chromatin Modifications and Their Function. 128(4):693-705] . The figure on the right enlists those histone-modifying enzymes whose specificity has been determined. There are at least eight distinct types of modifications found on histones(see the legend box on the top left of the figure). Enzymes have been identified for acetylation[Sterner, D.E., and Berger, S.L. (2000). Acetylation of histones and transcription-related factors. Microbiol. Mol. Biol. Rev. 64, 435–459] , methylation[Zhang, Y., and Reinberg, D. (2006). Transcription regulation by histone methylation: interplay between different covalent modifications of the core histone tails. Genes Dev. 15, 2343–2360] , demethylationcite journal |author=Klose RJ, Zhang Y |title=Regulation of histone methylation by demethylimination and demethylation |journal=Nat. Rev. Mol. Cell Biol. |volume=8 |issue=4 |pages=307–18 |year=2007 |pmid=17342184 |doi=10.1038/nrm2143] , phosphorylation[Nowak, S.J., and Corces, V.G. (2004). Phosphorylation of histone H3: a balancing act between chromosome condensation and transcriptional activation. Trends Genet. 20, 214–220] , ubiquitination[Shilatifard, A. (2006). Chromatin modifications by methylation and ubiquitination: implications in the regulation of gene expression. Annu. Rev. Biochem. 75, 243–269] , sumoylation[Nathan, D., Ingvarsdottir, K., Sterner, D.E., Bylebyl, G.R., Dokmanovic, M., Dorsey, J.A., Whelan, K.A., Krsmanovic, M., Lane, W.S., Meluh,P.B., et al. (2006). Histone sumoylation is a negative regulator in Saccharomyces cerevisiae and shows dynamic interplay with positiveactinghistone modifications. Genes Dev. 20, 966–976] , ADP-ribosylation[Hassa, P.O., Haenni, S.S., Elser, M., and Hottiger, M.O. (2006). Nuclear ADP-ribosylation reactions in mammalian cells: where are we today and where are we going? Microbiol. Mol. Biol. Rev. 70, 789–829] , deimination[Cuthbert, G.L., Daujat, S., Snowden, A.W., Erdjument-Bromage, H., Hagiwara, T., Yamada, M., Schneider, R., Gregory, P.D., Tempst, P., Bannister, A.J., and Kouzarides, T. (2004). Histone deimination antagonizes arginine methylation. Cell 118, 545–553] [Wang, Y., Wysocka, J., Sayegh, J., Lee, Y.H., Perlin, J.R., Leonelli, L., Sonbuchner, L.S., McDonald, C.H., Cook, R.G., Dou, Y., et al. (2004). Human PAD4 regulates histone arginine methylation levels via demethylimination. Science 306, 279–283] , and proline isomerization[Nelson, C.J., Santos-Rosa, H., and Kouzarides, T. (2006). Proline isomerization of histone H3 regulates lysine methylation and gene expression. Cell 126, 905–916] . For a detailed example of histone modifications in transcription regulation see RNA polymerase control by chromatin structureand table .
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