FIG. 1.

Regulatory mechanisms of the LsrR/phospho-AI-2 circuit in E. coli AI-2 uptake (modified from reference 70). The AI-2 uptake repressor LsrR represses many genes including the lsr operon (comprised of lsrACDBFG) and the lsrRK operon. AI-2 can be imported back inside the cell via LsrACDB. Imported AI-2 is processed as phospho-AI-2 via the kinase LsrK. Phospho-AI-2 has been reported to bind LsrR and relieve its repression of the lsr transporter genes, triggering their expression. This in turn stimulates additional AI-2 uptake. DPD, 4,5-dihydroxy-2,3-pentanedione.