Bradyrhizobium japonicum FixK2, a crucial distributor in the FixLJ-dependent regulatory cascade for control of genes inducible by low oxygen levels

Bradyrhizobium japonicum possesses a second fixK-like gene, fixK2, in addition to the previously identified fixK1 gene. The expression of both genes depends in a hierarchical fashion on the low-oxygen-responsive two-component regulatory system FixLJ, whereby FixJ first activates fixK2, whose product then activates fixK1. While the target genes for control by FixK1 are unknown, there is evidence for activation of the fixNOQP, fixGHIS, and rpoN1 genes and some heme biosynthesis and nitrate respiration genes by FixK2. FixK2 also regulates its own structural gene, directly or indirectly, in a negative way