Nitrogen control of the nif regulon in Klebsiella pneumoniae: involvement of the ntrA gene and analogies between ntrC and nifA.
AUTOR(ES)
Merrick, M J
RESUMO
The ntrC and nifA gene products of Klebsiella pneumoniae are transcriptional activators involved in general nitrogen control and nif-specific regulation, respectively. Multicopy plasmids expressing either ntrC or nifA from a foreign promoter were used to study the relationship between these two genes and ntrA. The nifA product substituted for ntrC product in activation of a number of genes including nifLA, hutUH and genes for arginine and proline utilisation. NtrC could not substitute for nifA in transcriptional activation of the nifHDKY operon. In ntrA- strains, neither the ntrC nor the nifA product functioned to activate transcription of nif promoters. In vitro transcription/translation studies with plasmid clones demonstrated similar levels of expression of ntrC and nifA in ntr+ and ntrA- S-30 extracts. Hence, lack of activator function in an ntrA mutant indicates that both the ntrC and nifA products require a functional ntrA for activity. When expressed from foreign promoters, both the ntrC and nifA products were active in conditions which would normally repress nif expression. Hence, the ntrA product was apparently not limiting in these conditions.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=555083Documentos Relacionados
- Mutational analysis of the Klebsiella pneumoniae nitrogenase promoter: sequences essential for positive control by nifA and ntrC (glnG) products.
- NtrC is required for control of Klebsiella pneumoniae NifL activity.
- Deletion analysis of the Klebsiella pneumoniae nitrogenase promoter: importance of spacing between conserved sequences around positions -12 and -24 for activation by the nifA and ntrC (glnG) products.
- Symbiotic nitrogen fixation by a nifA deletion mutant of Rhizobium meliloti: the role of an unusual ntrC allele.
- Products of nitrogen regulatory genes ntrA and ntrC of enteric bacteria activate glnA transcription in vitro: evidence that the ntrA product is a sigma factor.