Making and breaking heterochromatin
To fit the two-meter long DNA molecule into a cell nucleus that is only a few thousandths of a millimetre in size, long sections of the DNA must be strongly compacted. Epigenetic marks maintain these sections, known as heterochromatin. Scientists of the Max Planck Institute of Immunobiology and Epigenetics in Freiburg have now discovered two further mechanisms necessary for the formation of heterochromatin. The research group, led by Thomas Jenuwein, describes two novel enzymes, Prdm3 and Prdm16, which attach a methyl group to a particular packaging protein of the DNA. These epigenetic marks assure that heterochromatin, and with it the structure of the cell nucleus, remain intact. Moreover, in an additional study they have determined that transcription factors bind within heterochromatin and repress the output of non-coding RNA. In contrast to less densely compacted regions known as euchromatin, in which the transcription factors accumulate at specific sites, the binding sites...