Regolazione del gene della proteasi alcalina aprE mediato da CodY e la stringent response in Bacillus subtilis

In Bacillus subtilis, the aprE gene encodes the major secreted alkaline protease, whose transcription is governed by several factors, including CodY, a GTP- and branched chain amino acids-dependent global transcriptional regulator controlling more than 200 genes. Under conditions of nutritional stress, B. subtilis activates the stringent response, a mechanism that reprograms global gene expression. This pathway is mediated by the accumulation of the alarmone (p)ppGpp, synthesized by the Rel enzyme during amino acid starvation. As the levels of (p)ppGpp increase, the intracellular GTP pool is depleted and GTP synthesis is inhibited, leading to a sharp decline in one of CodY’s cofactors. To investigate whether the stringent response affects aprE expression and to determine the potential specific contribution of CodY, a transcriptional fusion between the aprE regulatory region and lacZ was introduced into a wild-type B. subtilis strain and its isogenic codY, rel and codY rel double mutants. The activity of aprE promoter was measured by β-galactosidase assays in chemically defined amino acid rich medium and into Difco sporulation medium. While the single mutants showed a reduction in aprE promoter activity compared to the wild type in sporulation medium, the double mutant showed a complete loss of promoter regulation across both media. Taken together, these findings are consistent with a model in which aprE transcription integrates nutritional and stress signals through the functional coupling of CodY and the stringent response.