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Enzyme removes methyl groups An enzyme that removes methyl groups from histones--the scaffolding proteins on which genomic DNA is wrapped for storage--has finally been identified. Chemical modifications made to histones regulate gene expression by controlling access to DNA. Pairs of opposing enzymes control the level of histone phosphorylation and acetylation. Although enzymes that transfer methyl groups to histone lysine and arginine side chains have been identified, enzymes that remove these methyl groups remain unknown. Now, a team led by C. David Allis of Rockefeller University and Scott A. Coonrod of Cornell University's Weill Medical College report that human peptidylarginine deiminase 4 converts methylarginine into citrulline, releasing methylamine (shown) [Science, published online Sept. 2, http://dx.doi.org/10.1126/science.1101400]. They show that the enzyme removes methylamines from histones both in vitro and in vivo, regulating both histone methylarginine levels and gene transcription. The observations support the long-held suspicion that histone methylation is reversible. |
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