Repressilator (synthetic gene oscillator)

Elowitz & Leibler (2000, Nature) constructed a synthetic oscillator in E. coli from three mutual repressor genes wired in a ring: LacI represses tetR; TetR represses cI; CI represses lacI. No gene product directly activates its own production, yet the circular negative feedback drives sustained oscillations in protein concentration with a period of ~150 minutes. The repressilator is a physical implementation of a relaxation oscillator: the mathematical operation is sustained limit-cycle dynamics, the same function realized by a CMOS ring oscillator or a Van der Pol circuit — but in living cells. Demonstrates that genetic regulatory networks can be designed as analog computing substrates, encoding functions (oscillation, bistability, logic) in DNA sequence. Speed: ~150 min period (transcription/translation kinetics). Capacity: single-frequency oscillator; frequency tunable by changing promoter strength or mRNA degradation rate.