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 E. coli K-12 and other enteric bacteria to N-limited growth. This protein, which is called NR1, for nitrogen regular I, was purified to about 95% purity from an overproducing strain. Purified NRI was identified as a dimer by gel filtration. NR1 specifically inhibited initiation of transcription from a DNA fragment containing the glnL promoter but was without effect on lacZ transcription. The intracellular concentration of NRI was determined under different growth conditions by using immunological techniques. The ratio of glutamine synthetase polypeptides, the product of the glnA gene, to NRI polypeptide was about 80:1. NRI was not rapidly degraded after ammonia shock, even though the ability to activate N-controlled systems was lost.