Microelectronic devices that contain biological components are typically used to interrogate biology(1,2) rather than control biological function. Patterned assemblies of proteins and cells have, however, been used for in vitro metabolic engineering(3-7), where coordinated biochemical pathways allow cell metabolism to be characterized and potentially controlled(8) on a chip. Such devices form part of technologies that attempt to recreate animal and human physiological functions on a chip(9) and could be used to revolutionize drug development(10). These ambitious goals will, however, require new biofabrication methodologies that help connect microelectronics and biological systems(11,12) and yield new approaches to device assembly and communication. Here, we report the electrically mediated assembly, interrogation and control of a multi-domain fusion protein that produces a bacterial signalling molecule. The biological system can be electrically tuned using a natural redox molecule, and its biochemical response is shown to provide the signalling cues to drive bacterial population behaviour. We show that the biochemical output of the system correlates with the electrical input charge, which suggests that electrical inputs could be used to control complex on-chip biological processes.