PURIFICATION AND INITIAL CHARACTERIZATION OF AHRC - THE REGULATOR OF ARGININE METABOLISM GENES IN BACILLUS-SUBTILIS

The arginine-dependent repressor-activator from Bacillus subtilis, AhrC, has been overexpressed in Escherichia coli and purified to homogeneity. AhrC, expressed in E. coli, is able to repress a Bacillus promoter (argC(p)), which lies upstream of the argC gene. The purified protein is a hexamer with a subunit molecular mass of 16.7 kDa. Its ability to recognize DNA has been examined in vitro using argC(p) in both DNase I and hydroxyl radical protection assays. AhrC binds at two distinct sites within the argC(p) fragment. One site, argC(O1), with the highest affinity for protein, is located within the 5' promoter sequences, whilst the other, argC(O2), is within the coding region of argC. The data are consistent with the binding of a single hexamer of AhrC to argC(O1) via four of its subunits, possibly allowing the remaining two subunits to bind at argC(O2) in vivo forming a repression loop similar to those observed for the E. coli Lac repressor.