Integrative plasmid vector for constructing single-copy reporter systems to study gene regulation in Rhizobium meliloti and related species.

The integrative system of phage 16-3 of Rhizobium meliloti 41 was shown to function in several bacterial species belonging to the Rhizobium, Bradyrhizobium, Azorhizobium, and Agrobacterium genera. It might also function in many other bacterial species provided that both the target site (attB) and the required host factor(s) are present. Here we report on the construction of a new integrative vector that can be utilized in gene regulation studies. It provides an opportunity to create a single-copy set-up for characterizing DNA-protein interactions in vivo, in a wide range of bacteria. To demonstrate the usefulness of the vector, transcription repression by binding of the C repressor protein of phage 16-3 to wild type operators was studied. The assay system provided highly reproducible quantitative data on repression.