Regulated expression of HPrK/P does not affect carbon catabolite repression of the xyn operon and of rocG in Bacillus subtilis

HPr kinase/phosphorylase (HPrK/P), a central metabolic regulator in many Gram-positive bacteria, reversibly phosphorylates HPr and Crh, thus controlling their activities as effectors of CcpA predominantly in carbon catabolite repression (CCR). We have placed the constitutively expressed hprK in its native chromosomal locus under anhydrotetracycline-dependent transcriptional control to establish the correlation between HPrK/P amounts and the efficiency of CCR in Bacillus subtilis. This resulted in about eightfold repression of HPrK/P expression but had no effect on CCR as monitored by xynP'-lacZ reporter gene expression and by analysis of RocG protein amounts. These results suggest that very small amounts of HPrK/P are sufficient for complete CCR and that control of HPrK/P activity depends only on the presence of effectors and not on the abundance of the enzyme.