Nature 436, 588-592 (28 July 2005) | doi:10.1038/nature03842; Received 11 April 2005; Accepted 19 May 2005

Optimality and evolutionary tuning of the expression level of a protein

Erez Dekel1 & Uri Alon1

  1. Department of Molecular Cell Biology and Department of Physics of Complex Systems, The Weizmann Institute of Science, Rehovot 76100, Israel

Correspondence to: Uri Alon1 Correspondence and requests for materials should be addressed to U.A. (Email: urialon@weizmann.ac.il).

Different proteins have different expression levels. It is unclear to what extent these expression levels are optimized to their environment. Evolutionary theories suggest that protein expression levels maximize fitness1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, but the fitness as a function of protein level has seldom been directly measured. To address this, we studied the lac system of Escherichia coli, which allows the cell to use the sugar lactose for growth12. We experimentally measured the growth burden13, 14 due to production and maintenance of the Lac proteins (cost), as well as the growth advantage (benefit) conferred by the Lac proteins when lactose is present. The fitness function, given by the difference between the benefit and the cost, predicts that for each lactose environment there exists an optimal Lac expression level that maximizes growth rate. We then performed serial dilution evolution experiments at different lactose concentrations. In a few hundred generations, cells evolved to reach the predicted optimal expression levels. Thus, protein expression from the lac operon seems to be a solution of a cost–benefit optimization problem, and can be rapidly tuned by evolution to function optimally in new environments.


These links to content published by NPG are automatically generated.


Strategies for cellular decision-making

Molecular Systems Biology Review (17 Nov 2009)

Phenotypic variation in bacteria: the role of feedback regulation

Nature Reviews Microbiology Review (01 Apr 2006)

See all 11 matches for Reviews


The econometrics of evolution

Nature Chemical Biology News and Views (01 Sep 2005)

Enzymes: Evolution in the Test-tube

Nature News and Views (27 Jul 1973)

See all 7 matches for News And Views