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Optimality and evolutionary tuning of the expression level of a protein

Summary: Optimality and evolutionary tuning of the
expression level of a protein
Erez Dekel1
& Uri Alon1
Different proteins have different expression levels. It is unclear to
what extent these expression levels are optimized to their environ-
ment. Evolutionary theories suggest that protein expression levels
maximize fitness111
, 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
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


Source: Alon, Uri - Departments of Molecular Cell Biology & Physics of Complex Systems, Weizmann Institute of Science


Collections: Biology and Medicine