FIGURE 1. Methylation-associated models of gene silencing.

From the following article:

Gene regulation: Code of silence

Judd C. Rice and C. David Allis

Nature 414, 258-261(15 November 2001)

doi:10.1038/35104721

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a, DNA methylation. Cytosine nucleotides are methylated by a DNA methyltransferase, increasing the affinity of methyl-binding proteins for DNA. Some of these proteins associate with repressive complexes that contain histone deacetylases, resulting in the removal of acetyl groups from lysine (K) residues in the tails of histone proteins, and gene silencing. b, Histone methylation. Acetyl groups must be removed before lysine residue 9 on histone H3 can be methylated by a histone methyltransferase. Heterochromatin-associated proteins preferentially bind methylated lysine 9, leading to gene silencing. c, DNA methylation and histone methylation. Tamaru and Selker1 show that methylation of histone H3 lysine 9 is required for subsequent DNA methylation and gene silencing in filamentous fungi. It is not known whether or not the histone and DNA methyltransferases interact.

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