Scientists have discovered a new mechanism that protects active genes from being silenced during cell division. They found that two variants of the same protein can distinguish active and inactive areas of the genome. The two variants differ by just one amino acid, circled here. Researchers captured the atomic structure of the two variants using a kind of molecular photography, shown here. They discovered that the single amino acid change is recognized by an enzyme (in red and blue here) that adds a silencing mark to only one variant (indicated with an arrow), instructing the cell to keep those areas of the genome inactive.