Interaction of GlnK with the GAF domain of Herbaspirillum seropedicae NifA mediates NH4+-regulation

► NifA protein is responsible for the transcriptional regulation of nitrogen fixation. ► The activity of Herbaspirillum seropedicae NifA is regulated by oxygen and fixed nitrogen. ► The GAF domain of NifA inhibits its activity in response to fixed nitrogen. ► The GlnK protein transduces the fixed nitrogen availability to the GAF domain. ► GlnK interacts with GAF domain in vitro.