In-trans regulation of the N-truncated-NIFA protein of Herbaspirillum seropedicae by the N-terminal domain

The NifA protein is responsible for transcription activation of nif genes i n the endophytic diazotroph Herbaspirillum seropedicae. When expressed in E scherichia coli this NifA protein is unable to activate the transcription o f a Klebsiella pneumoniae nifH::lacZ fusion. However, a form of NifA lackin g the N-terminal domain did activate transcription and its activity was not inhibited by ammonium. In this work we show that when expressed separately , the N-terminal domain of H. seropedicae NifA protein can restore ammonium control of the N-truncated NifA activity in E. coli. This effect is depend ent on the relative concentrations of the N-terminal domain and the N-trunc ated protein and suggests that the N-terminal domain behaves in this respec t in a manner similar to that of NifL of the gamma proteobacteria. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Sc ience B.V. All rights reserved.