Tuning of mRNA stability through altering 3'-UTR sequences generates distinct output expression in a synthetic...

Synthetic biological circuits that can generate outputs with distinct expression dynamics are useful for a variety of biomedical and industrial applications. We present a method to control output dynamics by altering output mRNA decay rates. Using oscillatory expression of the transcription factor p53 as the circuit regulator, we use two approaches for controlling target gene transcript degradation rates based on the output gene's 3'-untranslated region (3'-UTR): introduction of copies of destabilizing AU-rich elements into the 3'-UTR or swapping in naturally occurring 3'-UTRs conferring different transcript stabilities. As a proof of principle, we apply both methods to control the expression dynamics of a fluorescent protein and visualize the circuit output dynamics in single living cells. We then use the naturally occurring 3'-UTR approach to restore apoptosis in a tunable manner in a cancer cell line deficient for caspase-3 expression. Our method can be readily adapted to regulate multiple outputs each with different expression dynamics under the control of a single naturally occurring or synthetically constructed biological oscillator.