The Bacillus subtilis NatK–NatR two-component system regulates expression of the natAB operon encoding an ABC transporter for sodium ion extrusion

A previous microarray analysis suggested that multicopy yccH, encoding a function-unknown response regulator, enhances expression of natAB, which encodes a two-gene ATP-binding cassette transporter involved in the extrusion of sodium ions. The two-component regulatory system YccG-YccH was therefore renamed NatK-NatR. Here, this observation was confirmed by a lacZ fusion analysis using a strain carrying natA-lacZ. Further, in both natK and natR mutants, natA-lacZ expression was completely abolished, indicating that the NatK-NatR system positively regulates the expression of natAB. In a gel retardation analysis, NatR bound to the natA promoter region. Using purified His-tagged NatR, DNase I footprinting analysis of the natA promoter region suggested that a direct repeat of [TTCA(G)CGACA], separated by a 12 bp space, would be recognized by NatR. Deleted and mutagenized promoter regions of natA were analysed using a lacZ fusion, and it was confirmed that the direct repeat is critical for natA activation by NatR.