AN EXTRACELLULAR FACTOR REGULATES EXPRESSION OF SDIA, A TRANSCRIPTIONAL ACTIVATOR OF CELL-DIVISION GENES IN ESCHERICHIA-COLI

The sdiA gene codes for a protein that regulates expression of the fts QAZ cluster of essential cell division genes of Escherichia coli. SdiA up regulates the ftsQ2p promoter that initiates transcription into th e ftsQAZ cluster, In this paper, we report that expression of sdiA is itself regulated by a factor that is released into the growth medium b y E. coli. When medium that had previously supported growth of E. coli (conditioned medium) was used to support growth of an indicator E. co li strain that contained an sdiA-lacZ transcriptional reporter, there was a 50 to 80% decrease in sdiA expression as monitored by beta-galac tosidase activity. The down-regulation of P-sdiA was associated with a decrease in expression of the SdiA target promoter ftsQ2p, as monitor ed by expression of an ftsQ2p-lacZ transcriptional fusion, An effect o f conditioned medium on ftsQ2p expression was not seen when the wild-t ype sdiA gene was disrupted by insertional mutagenesis, indicating tha t the effect on ftsQ2p expression was secondary to the down-regulation of P-sdiA. Conditioned medium had no effect on expression of P-lac, P -rpoS, or several other promoters associated with the ftsQAZ gene clus ter (ftsQlp and ftsZI-4p). This suggests that the response is specific for P-sdiA and for promoters that are regulated by the sdiA gene prod uct and that cell-to-cell signalling may play a role in regulating exp ression of this group of genes.