Mutations in the Bacillus subtilis purine repressor that perturb PRPP effector function in vitro and in vivo

The Bacillus subtilis pur operon repressor (PurR) has a PRPP (5-phosphoribo syl 1-pyrophosphate) binding motif at residues 199-211. Two PurR PRPP bindi ng region mutations (D203A and D204A) were constructed, and the effects on binding of repressor to the pier operon control site in vitro and on regula tion of pur operon expression in vivo were investigated. PRPP significantly inhibited the binding of wild-type but not mutant PurR to pur operon contr ol site DNA. In strains with the D203A and D204A mutations, pur operon expr ession in vivo was super-repressed by addition of adenine to the growth med ium. These results support the role of PRPP in modulating the regulatory fu nction of PurR in vivo. YabJ, the product of the distal gene in the bicistr onic purR operon, is also required for PurR function in vivo.