cover illustration The lactose repressor and its cognate operator were subjected to directed evolution in an attempt to create a higher affinity complex which would reduce background expression under repressing conditions. Here the interactions between the key residues of the wild type recognition helix (Y17, Q18 and R22) and a half site of the operator are shown.These critical residues were randomized and the library was screened looking for mutants which could repress transcription of a reporter gene downstream of the operator site.A single mutation, Q18M, was identified which greatly reduced background expression from the natural operator. For further details see Daber and Lewis pp. 673-683.
[Table of Contents]