Genetic analysis of Rhizobium meliloti bacA-phoA fusion results in identification of degP: two loci required for symbiosis are closely linked to degP.
The function of the Rhizobium meliloti bacA gene, which is a homolog of the Escherichia coli sbmA gene, is required for an intermediate step in nodule development. A strain carrying the bacA386::TnphoA fusion was mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine, and three mutants that had higher levels of alkaline phosphatase activity were identified. The mutations in these strains were recessive and mapped to the same genetic locus. The gene affected by these mutations was identified and sequenced and was found to be a homolog of the E. coli degP gene, which encodes a periplasmic endopeptidase. Although degP function is important for the virulence of certain intracellular pathogens of mammals, it is not required for the R. meliloti-alfalfa symbiosis. The genetic analyses involving degP were complicated by the presence of a locus immediately upstream of depP that was lethal when present in multiple copies in a DegP- background. R. meliloti derivatives carrying insertion mutations in this locus displayed an N,N,N',N'-tetramethyl-p-phenylenediamine oxidase-negative phenotype, elicited the formation of white cylindrical nodules that did not fix nitrogen, and grew slowly in rich medium, suggesting that the locus was a cyc gene encoding a protein involved in the biosynthesis of a component or components of a respiratory chain. The previously identified fix-382::TnphoA, which similarly causes the formation of white cylindrical nodules that do not fix nitrogen, was shown to affect a gene that is separate from this cyc gene but extremely closely linked to it.
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
J
J
Glazebrook
A
A
Ichige
G C
GC
Walker
D000469:Alkaline Phosphatase / Q000096:biosynthesis; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D004579:Electron Transport; D005798:Genes, Bacterial; D006360:Heat-Shock Proteins; D008565:Membrane Proteins / Q000235:genetics*; D026901:Membrane Transport Proteins; D008769:Methylnitronitrosoguanidine; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D033903:Periplasmic Proteins; D012697:Serine Endopeptidases / Q000235:genetics*; D016962:Sinorhizobium meliloti / Q000235:genetics* / Q000378:metabolism; D013559:Symbiosis
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033903:Periplasmic Proteins; C082397:bacA protein, Rhizobium meliloti; D008769:Methylnitronitrosoguanidine; D000469:Alkaline Phosphatase; C061682:DegP protease; D012697:Serine Endopeptidases