A novel response-regulator is able to suppress the nodulation defect of a Bradyrhizobium japonicum nodW mutant

Mol Gen Genet. 1993 Dec;241(5-6):531-41. doi: 10.1007/BF00279895.


The two-component regulatory system Nod-VW of Bradyrhizobium japonicum is essential for the nodulation of the legume host plants Vigna radiata, V. unguiculata and Macroptilium atropurpureum. The NodV protein shares homology with the sensor-kinases, whereas the NodW protein is a member of the response-regulator class. We report here the identification of a new B. japonicum DNA region that is able to suppress the phenotypic defect of a nodW mutant, provided that this region is expressed from a foreign promoter. The minimal complementing region, which itself is not essential for nodulation in a nodW+ background, consists of one gene designated nwsB (nodW-suppressor). The deduced amino acid sequence of the nwsB gene product shows a high degree of homology to NodW. The nws B gene is preceded by a long open reading frame, nwsA, whose putative product appears to be a sensor-kinase. Downstream of nwsB, an open reading frame encoding a second putative response-regulator was identified. Interspecies hybridization revealed the presence of nwsAB-like DNA also in other Bradyrhizobium strains. Using nwsB'-'lacZ fusions, the nwsB gene was found to be expressed rather weakly in B. japonicum. This low level of expression is obviously not sufficient to compensate for a nodW- defect, whereas strong overexpression of nwsB is a condition that leads to suppression of the nodW- mutation.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics*
  • Base Sequence
  • DNA, Bacterial / genetics
  • Genes, Bacterial*
  • Genes, Regulator*
  • Genes, Suppressor*
  • Molecular Sequence Data
  • Restriction Mapping
  • Rhizobiaceae / genetics*
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Species Specificity
  • Symbiosis


  • Bacterial Proteins
  • DNA, Bacterial

Associated data

  • GENBANK/Z22637