DNA sequence determinants of lambda repressor binding in vivo.

The critical operator determinants for lambda repressor recognition have been defined by analyzing the binding of wild-type repressor to a set of mutant operators in vivo. Base pair substitutions at six positions within the lambda operator half-site impair binding severely, and define these base pairs as critical for operator function. One mutant operator binds repressor better than the consensus operator, and is a superoperator. The model proposed by M. Lewis in 1983 for the binding of lambda repressor to its operator accurately predicts the observed operator requirements for binding in vivo, with several minor exceptions. The order of affinities of the six natural lambda operators has also been determined.