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Infection and Immunity, October 2008, p. 4581-4591, Vol. 76, No. 10
0019-9567/08/$08.00+0     doi:10.1128/IAI.00337-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Identification of a Hypervariable Region Containing New Legionella pneumophila Icm/Dot Translocated Substrates by Using the Conserved icmQ Regulatory Signature{triangledown} ,{dagger}

Tal Zusman, Elena Degtyar, and Gil Segal*

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

Received 13 March 2008/ Returned for modification 27 April 2008/ Accepted 1 August 2008

Legionella pneumophila is an intracellular pathogen that has been shown to utilize the Icm/Dot type IV secretion system for pathogenesis. This system was shown to be composed of Icm/Dot complex components, accessory proteins, and a large number of translocated substrates. In this study, comparison of the icmQ regulatory regions from many Legionella species revealed a conserved regulatory sequence that includes the icmQ –10 promoter element. Mutagenesis of this conserved regulatory element indicated that each of the nucleotides in it affects the level of expression of the icmQ gene but not in a uniform fashion. A genomic analysis discovered that four additional genes in L. pneumophila contain this conserved regulatory sequence, which was found to function similarly in these genes as well. Examination of these four genes indicated that they are dispensable for intracellular growth, but two of them were found to encode new Icm/Dot translocated substrates (IDTS). Comparison of the genomic regions encoding these two IDTS among the four available L. pneumophila genomic sequences indicated that one of these genes is located in a hypervariable genomic region, which was shown before to contain an IDTS-encoding gene. Translocation analysis that was performed for nine proteins encoded from this hypervariable genomic region indicated that six of them are new IDTS which are translocated into host cells in an Icm/Dot-dependent manner. Furthermore, a bioinformatic analysis indicated that additional L. pneumophila genomic regions that contain several neighboring IDTS-encoding genes are hypervariable in gene content.

* Corresponding author. Mailing address: Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel. Phone: 972-3-6405287. Fax: 972-3-6409407. E-mail: GilS{at}tauex.tau.ac.il

{triangledown} Published ahead of print on 11 August 2008.

{dagger} Supplemental material for this article may be found at http://iai.asm.org/.

Editor: J. B. Bliska

Infection and Immunity, October 2008, p. 4581-4591, Vol. 76, No. 10
0019-9567/08/$08.00+0     doi:10.1128/IAI.00337-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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