Chromatin (image) Max-Planck-Gesellschaft Caption Methylation of histones within heterochromatin: The enzymes Prdm3 and Prdm16 attach a methyl group to histone H3. In the cell nucleus, Suv39h attaches two further methyl groups. The cell appears to require this triple methylation for heterochromatin to be stable. Credit Art For Science Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.