Fig 6.
Model of the role of MecA in competence regulation of S. thermophilus. The alternative sigma factor σX, encoded by comX, is recognized and sequestrated by MecA, which also binds the ClpC ATPase subunit of the Clp machinery. This ternary complex interacts with the serine protease ClpP, leading to the degradation of σX by ClpCP, resulting in a small amount of free σX, which is insufficient to induce the transcription of late com genes. However, when conditions are appropriate for competence development, σX accumulates above a critical threshold, allowing its association with the core RNA polymerase for the specific transcription of late com genes.