Selection of lac gene fusions in vivo: ompR-lacZ fusions that define a functional domain of the ompR gene product.

We describe a simple method for selecting Escherichia coli mutants that carry gene fusions between a cloned gene and lacZ. We test this technique with the ompR gene, which codes for a positive regulatory factor in porin synthesis. A number of OmpR-LacZ hybrid proteins are examined, and several unusual phenotypes associated with these protein fusions are described. Evidence is presented to support the two-domain model for ompR proposed previously (Hall and Silhavy, J. Mol. Biol. 151:1-15). In addition, one of the ompR-lacZ fusions exhibits a dominant OmpR- phenotype. The utility of isolating a series of lacZ gene fusions to any target gene is discussed.