Use of Chimeric Proteins to Investigate the Role of the GAF Domain of Herbaspirillum seropedicae NifA in the Response to Fixed Nitrogen
Herbaspirillum seropedicae (Hs) NifA activity is controlled by external ammonium and O2 levels. Ammonium control involves the N-terminal GAF domain and PII-like signal-transduction proteins (Souza et al., 1999). When expressed separately the N-terminal GAF domain of NifA inhibits the activity of AAA+ and C-terminal domains in the presence of excess ammonium (Monteiro et al., 1999). To study the response of the N-terminal GAF domain to ammonia, we constructed chimeric proteins between the GAF domain of Hs NifA and the AAA+ and C-terminal domains of K. pneumoniae (Kp) and A. vinelandii (Av) NifA, which are not regulated by O2 (Dixon, 1998).