Activation of Klebsiella pneumoniae and Rhizobium meliloti nitrogenase promoters by gln (ntr) regulatory proteins.

Abstract
The expression, in different Escherichia coli gln (ntr) mutants, of fusions (constructed in vitro) of the nifHDK (nitrogenase) promoters from K. pneumoniae and R. meliloti to E. coli lacZ was studied. Derepression of the K. pneumoniae nifH::lacZ fusion requires the glnF (ntrA) gene product in addition to the K. pneumoniae nifA gene product, indicating that regulation of the K. neumoniae nif genes is more closely integrated with the overall N control system than previously demonstrated. Derepression of the R. meliloti nifH::lacZ fusion in E. coli by the K. pneumoniae nifA gene product exhibits the same requirement for glnF. Derepression of the R. meliloti nifH::lacZ fusion, but not the K. pneumoniae nifH::lacZ fusion, can be mediated by the glnG (ntrC) gene product, suggesting that the gln regulatory genes might directly regulate the symbiotic N2 fixation genes in Rhizobium.