RT Journal Article SR Electronic T1 Design and implementation of a synthetic biomolecular concentration tracker JF bioRxiv FD Cold Spring Harbor Laboratory SP 000448 DO 10.1101/000448 A1 Victoria Hsiao A1 Emmanuel LC de los Santos A1 Weston R. Whitaker A1 John E. Dueber A1 Richard M. Murray YR 2013 UL http://biorxiv.org/content/early/2013/12/10/000448.abstract AB As a field, synthetic biology strives to engineer increasingly complex artificial systems in living cells. Active feedback in closed loop systems offers a dynamic and adaptive way to ensure constant relative activity independent of intrinsic and extrinsic noise. In this work, we design, model, and implement a biomolecular concentration tracker, in which an output protein tracks the concentration of an input protein. Using synthetic scaffolds built from small, modular protein-protein interaction domains to colocalize a two-component system, the circuit design relies on a single negative feedback loop to modulate the production of the output protein. Using a combination of modeling and experimental work, we show that the circuit achieves real-time protein concentration tracking in Escherichia coli and that steady state outputs can be tuned.