Mutations in the CI gene of lambda bacteriophage which retain immunity and confer a rex phenotype

Among lambda N - DNA - defective lysogens able to give the antiimmune phase mutations have been found which do not affect appreciably lysogenization frequency and plaque turbidity, but show a rex - phenotype. These mutations complement classical rex - mutations, which map on the left side of the immunity region, and seem to imply a role of CI product in rex function.