The groups of Ivan Dikic and Masato Akutsu have moved closer in understanding how a novel form of protein modification, the linear ubiquitination, controls central pathways of immunity and inflammation. In a collaborative effort, they showed that the two enzymes responsible for assembling and disassembling linear ubiquitin chains are contained in one complex. By structural analysis, they managed to decipher the molecular details of the interaction between these two key enzymes and were able to show how the opposing activities of the complex are controlled. Their results are published in the current edition of Molecular Cell online.