The response regulator CpxR directly regulates the expression of several Legionella pneumophila icm/dot components as well as new translocated substrates

Department of Molecular Microbiology & Biotechnology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, ISRAEL

^* To whom correspondence should be addressed. Email: GilS{at}tauex.tau.ac.il.

	Abstract

Legionella pneumophila has been shown to utilize the icm/dot type IV secretion system for pathogenesis. This system was shown to be composed from icm/dot complex components, accessory proteins as well as a large number of translocated substrates. Bioinformatic analysis of the regulatory regions of all these genes revealed that several icm/dot genes as well as two icm/dot translocated substrates contain the conserved CpxR regulatory element, a regulator that has been shown before to control the expression of the icmR gene. Experimental analysis which included comparison of gene expression between L. pneumophila wild type and a cpxR deletion mutant, construction of mutations in the CpxR conserved regulatory elements, controlled expression studies as well as mobility shift assays, demonstrated the direct relation between the CpxR regulator and the expression of these genes. Furthermore, genomic analysis identified nine additional genes that contain a putative CpxR regulatory element, five of these genes (two-legA genes and three-ceg genes) were suggested before as putative icm/dot translocated substrates. The three ceg genes identified, that were shown before to contain a putative PmrA regulatory element, were found here to be regulated by both CpxR and PmrA. The other six genes (two-legA genes and four new genes) were found to be regulated by CpxR. Moreover, using the CyaA translocation assay these nine genes were found to be translocated into host cells in an Icm/Dot dependent manner. Our results establish the CpxR regulator as a fundamental regulator of the icm/dot type IV secretion system in L. pneumophila.