Requirements for transcriptional activation in vitro of the nitrogen-regulated glnA and nifLA promoters from Klebsiella pneumoniae: dependence on activator concentration.

Three proteins involved in nitrogen regulation in Klebsiella pneumoniae, NTRA, NTRB and NTRC, have been purified. In a defined in vitro system all three NTR proteins are required for initiation of transcription at the ntr activatable glnA and nifLA promoters. However, in crude S-30 extracts, transcription from the glnA promoter, but not the nifLA promoter, can be activated in the absence of NTRB. A higher concentration of NTRC is required for activation of nifLA transcription than for glnA transcription. Sequences located between -227 and -158 with respect to the nifL transcription start site are required for efficient activation of the nifLA promoter in vitro.