Transcription Analysis of the Bacillus subtilis PucR Regulon and Identification of a cis-Acting Sequence Required for PucR-Regulated Expression of Genes Involved in Purine Catabolism

The PucR protein of Bacillus subtilis has previously been suggested to regulate the expression of 15 genes, pucABCDE, pucFG, pucH, pucI, pucJKLM, pucR, and gde, all of which encode proteins involved in purine catabolism. When cells are grown under nitrogen-limiting conditions, the expression of these genes is induced and intermediary compounds of the purine catabolic pathway affect this expression. By using pucR deletion mutants, we have found that PucR induces the expression of pucFG, pucH, pucI, pucJKLM, and gde while it represses the expression of pucR and pucABCDE. Deletions in the promoters of the five induced operons and genes combined with bioinformatic analysis suggested a conserved upstream activating sequence, 5′-WWWCNTTGGTTAA-3′, now named the PucR box. Potential PucR boxes overlapping the −35 and −10 regions of the pucABCDE promoter and located downstream of the pucR transcription start point were also found. The positions of these PucR boxes are consistent with PucR acting as a negative regulator of pucABCDE and pucR expression. Site-directed mutations in the PucR box upstream of pucH and pucI identified positions that are essential for the induction of pucH and pucI expression, respectively. Mutants with decreased pucH or increased pucR expression obtained from a library of clones containing random mutations in the pucH-to-pucR intercistronic region all contained mutations in or near the PucR box. The induction of pucR expression under nitrogen-limiting conditions was found to be mediated by the global nitrogen-regulatory protein TnrA. In other gram-positive bacteria, we have found open reading frames that encode proteins similar to PucR located next to other open reading frames encoding proteins with similarity to purine catabolic enzymes. Hence, the PucR homologues are likely to exert the same function in other gram-positive bacteria as PucR does in B. subtilis.