Upon infection cells manage to quickly switch from normal operation to immune reaction in a matter of minutes. This innate immunity requires a cellular signal cascade that activates antimicrobial or antiviral gene expression. Scientists led by Thomas Decker at the Max Perutz Labs have discovered that an alternative version of the activator of antimicrobial gene expression is constantly present on DNA. A molecular switch between the alternative and the regular version enables a quick onset of the immune response. The findings are published in the journal “Nature Communications”.