The glnB region of the Escherichia coli chromosome

We present sequences of the glnB gene of Escherichia coli and of two open reading frames (ORFs) located directly upstream of glnB and transcribed in the same direction. The major transcriptional start sites for glnB are located between ORF-2 and glnB, but some transcription of glnB is initiated at the promoter for ORF-1. The putative amino acid sequence of the ORF-2 product has high homology to that of response regulators which by phosphorylation acquire the ability to activate transcription of sigma 54-dependent promoters. The product of ORF-1 showed no similarity to other known proteins. The product of neither ORF-1 nor ORF-2 is necessary for the ability of PII, the product of glnB, to bring about the repression of glutamine synthetase in response to nitrogen excess. On the other hand, the product of hmpA, a gene located on the other side of glnB and transcribed in the opposite direction, appears to play an auxiliary role in this process.