Isolation of the nitrogen assimilation regulator NR_I, the product of the glnG gene of Escherichia coli

Abstract

The product of the glnG gene, a member of the complex glnALG operon, is an essential component in the response of Escherichia coli K-12 and other enteric bacteria to nitrogen-limited growth. We have purified this protein which we propose to call “NR_I,” for nitrogen regulator I, to about 95% purity from an overproducing strain. Purified NR_I was identified as a dimer by gel filtration. NR_I specifically inhibited initiation of transcription from a DNA fragment containing the glnL promoter but was without effect on lacZ transcription. We determined the intracellular concentration of NR_I under different growth conditions by using immunological techniques. The ratio of glutamine synthetase polypeptides, the product of the glnA gene, to NR_I polypeptides was about 80:1. NR_I was not rapidly degraded after ammonia shock, even though the ability to activate nitrogen-controlled systems was lost.

• nitrogen regulation
• transcription in vitro
• glnL promoter