Sept 15 (Thursday) Erez Dekel (The Weizmann Institude of Science)

Optimality and evolutionary tuning of the expression level of a protein

Abstract:

Different proteins have different expression levels. Are these levels a
result of historical accident, or are they optimized to best function in
their environment? If the latter is correct, can one formulate a theory to
explain the expression level in a given environment, and to predict how
rapidly these levels can be tuned by evolution once conditions change? To
address this, we studied the well-known lac operon of E. coli, which
utilizes the sugar lactose. We experimentally measured the growth burden
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 cost and benefit fitness function predicts that in a given
lactose environment there exists an optimal lac expression which 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 appears to be a solution of a simple
cost-benefit optimization problem, and can be rapidly tuned by evolution
to function optimally in new environments.