Interaction of bacteriophage lambda repressor with nonoperator DNA containing single-strand gaps.

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Abstract
In direct binding assays, purified .lambda.ind+ repressor displayed high affinity for nonoperator DNA containing single-strand gaps. Its affinity for this same DNA but completely double-stranded, nicked, or denatured was considerably lower. Purified .lambda.ind- repressor had 1/10th the affinity for the gapped DNA, a level comparable to that of purified lac repressor. In the presence of limiting amounts of ind+ repressor nonoperator DNA containing gaps competed effectively with .lambda. DNA for binding of repressor. A previous model of .lambda. induction based on the assumption that this phenomenon involves the binding of repressor to lesions in the host [Escherichia coli] DNA, is reevaluated in the light of present data.