Pseudoreversion of lactose operator-constitutive mutants.

A set of pseudorevertants of lactose operator-constitutive (lacOc) mutant has been obtained. Analysis of a subset of these pseudorevertants indicates that, in some cases, the secondary mutation alters the lactose repressor (lacl gene product), whereas in others it seems to have occurred in the lactose operator (lacO) itself. Of the lacl gene mutations, the lacl8 mutation, already known to suppress all lacOc mutations nonspecifically, was recovered by a selection technique developed for this study. However, two additional lacl gene mutants were selected which appear to suppress lacOc sequences in a more-or-less specific fashion; repressor interaction with some operator sequences is facilitated, whereas the binding with lacO+ and others is attenuated concomitantly.