Figure 8. Model of regulatory circuitry of pLS20 conjugation genes.

A. Repressed state due to Rco_LS20. Gene rco_LS20 (red arrow, rco) encoding the master repressor of conjugation genes Rco_LS20 is divergently transcribed from the putative conjugation operon encompassing genes 28 to 74 (light blue arrows). Rco_LS20 inhibits expression of the conjugation genes by repressing a promoter, P_c, located upstream of gene 28, the first gene of the putative conjugation operon (our unpublished results). B. Activation of conjugation by Rap_LS20 anti-repressor. Gene _rapLS20 (green arrow, rap) encodes the anti-repressor of Rco_LS20 leading to de-repression of the conjugation genes. C. Repressed state due to inactivation of Rap_LS20 by signaling peptide Phr*_LS20. Gene phr_LS20 (brown arrow, phr) encodes a pre-pro-protein of 44 residues. This protein is subject to an export-maturation-import route. The mature pentapeptide inhibits activity of the Rap_LS20 anti-repressor protein. For simplicity, import of the mature peptide has been shown into the cell producing the peptide. Grey cylinders labeled sec and imp, respectively, indicate the secretion and import routes. Extracellular processing of the secreted peptide is symbolized by the brown interrupted rectangle. QS, quorum sensing.