All cells in our body carry the dictionary of genetic information, the human genome. However, their shape and function are determined by which genes are read from this dictionary and translated into proteins, the building blocks of a cell. The “reading” of active genes starts with their transcription into so-called messenger RNAs (mRNAs), a process that is controlled through a complex network of transcriptional regulators. Mutations in these regulators can alter the function and identity of cells and thereby lead to cancer and other human diseases. At the same time, blocking abnormal transcription can kill cancer cells, which makes some transcriptional regulators attractive targets for drug development.