Identification and phenotypical characterization of a cluster of fix genes, including a nif regulatory gene, from Rhizobium leguminosarum PRE

✍ Scribed by Schetgens, Resie M. P. ;Hontelez, Jan G. J. ;van den Bos, Rommert C. ;van Kammen, Albert

• Book ID: 104770464
• Publisher: Springer
• Year: 1985
• Tongue: English
• Weight: 782 KB
• Volume: 200
• Category: Article
• ISSN: 0026-8925
• DOI: 10.1007/bf00425719

✦ Synopsis

A nif regulatory gene in R. leguminosarum PRE was identified by interspecies DNA hybridization and sitedirected Tn5 mutagenesis. Significant homology was found with the K. pneumoniae nifA locus, a R. meliloti symbiotic regulatory gene and E. coli ntrC; Tn5 insertions within this nifA gene inhibit the expression of the nifHDK operon, encoding synthesis of the nitrogenase polypeptides.

Specific DNA hybridization also was detected between a downstream adjacent part of the PRE sym plasmid and the R. leguminosarum 248 fixZ gene, a homologue of the K. pneumoniae nifB locus. To detect further fix genes we investigated a region of the sym plasmid which is localized within a short distance upstream from the nifA gene and is transcribed selectively at a high rate during symbiosis. This approach revealed the existence of a fix cluster in which Tn5-mutations cause a Fix phenotype although wild-type levels of nitrogenase synthesis were detectable. In a sym plasmid fragment, which is immediately upstream adjacent to the nifA locus and only moderately expressed in Rhizobium bacteroids, a second fix gene conferring the same symbiotic phenotype was detected.