Theory 50/Synthetic Biology
Burden Is an Expression Ratio
The claim
The fitness burden of an engineered circuit is set by the ratio of heterologous to native protein expression, not by heterologous expression alone.
01The mechanism
Burden arises from competition for ribosomes and amino acids; the share of the proteome diverted sets the cost, which is a ratio to what the cell needs.
02Predictions
- P1Burden should track the ratio.
- P2Absolute expression should mispredict across growth rates.
03Refutation
Burden tracking absolute expression would remove the ratio.