Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins” to the damaged parts within the DNA. To do this, an elaborate protein language has evolved. Now scientists from the Max Planck Institute for Biology of Ageing in Cologne have discovered the way a new letter of this alphabet is used in cells. This novel protein modification, called serine ADP-ribosylation, has been overlooked by scientists for decades. This finding reveals how important discoveries may be hidden in scientific “blind spots”.