DNA binding activity of NtrC from Rhizobium grown on different nitrogen sources

Abstract
The DNA‐binding activity of the NtrC protein can be demonstrated in gel retardation assays with concentrated protein extracts of Rhizobium etli. Using extracts from either the wild type or a ntrC mutant strain and an antiserum raised against the NtrC protein, we demonstrate specific binding of NtrC to the upstream regulatory region of the glnII gene, where two putative NtrC‐binding sites are present. KNO3‐grown bacteria contain less NtrC protein and more NtrC‐binding activity than NH4Cl‐grown bacteria, thus showing that with this protocol it is possible to detect changes in NtrC‐binding activity. The advantages of this assay system in comparison with that using pure proteins is discussed.