NTRBC-DEPENDENT EXPRESSION FROM THE RHIZOBIUM-MELILOTI DCTA PROMOTER IN ESCHERICHIA-COLI

Effects of the two-component sensor-regulator pairs DctBD and NtrBC up on the expression of a dctA::phoA fusion from Rhizobium meliloti were determined under excess and limiting nitrogen concentrations in Escher ichia coli. Results indicated that NtrBC affected transcription from t he dctA promoter on a number of regulatory levels and under different physiological conditions in the heterologous host. However, NtrBC-depe ndent cross-talk was not observed in free-living R. meliloti under the conditions tested. Comparisons of the predicted amino acid sequences of DctD and NtrC from various sources indicated a specific region of t he NtrC from rhizobia, which may have diverged from a consensus NtrC/D ctD sequence to minimise interference between the two component system s, NtrBC and DctBD.