Rearrangements between the operators in the bacteriophage lambda

The left operator mutant lambda v2s develops poorly during infection as a result of constitutive expression of the left operon. A revertant of lambda v2s, designated lambda iri, was found to contain an inversion of the cI region with the inversion endpoints to be within the lambda operators OL and OR. Formation of the inversion is facilitated by a translocation of right operator OcR mutant sequence to the left operator in lambda v2s. The inversion in lambda iri positions wild-type OR sequence at OL returning control of the left operon to repression by the lambda cro repressor.