When genetic information is read from the genetic blueprint DNA, RNA polymerase II translates it into RNA molecules. The C-terminal domain, abbreviated as CTD, is an important area of the polymerase molecule. It conveys information to the polymerase about how the genetic code should be copied and processed. To do this, the enzyme P-TEFb attaches molecular messages in the form of phosphate residues to certain positions within the CTD. Scientists at the Max Planck Institute of Molecular Physiology in Dortmund have described the pattern, on the basis of which P-TEFb completes this process.