RT Journal Article SR Electronic(1) A1 Grall, Nathalie A1 Livny, Jonathan A1 Waldor, Matthew A1 Barel, Monique A1 Charbit, Alain A1 Meibom, Karin L.YR 2009 T1 Pivotal role of the Francisella tularensis heat-shock sigma factor RpoH JF Microbiology, VO 155 IS 8 SP 2560 OP 2572 DO https://doi.org/10.1099/mic.0.029058-0 PB Microbiology Society, SN 1465-2080, AB Francisella tularensis is a highly infectious pathogen that infects animals and humans to cause the disease tularemia. The primary targets of this bacterium are macrophages, in which it replicates in the cytoplasm after escaping the initial phagosomal compartment. The ability to replicate within macrophages relies on the tightly regulated expression of a series of genes. One of the most commonly used means of coordinating the regulation of multiple genes in bacteria consists of the association of dedicated alternative sigma factors with the core of the RNA polymerase (RNAP). In silico analysis of the F. tularensis LVS genome led us to identify, in addition to the genes encoding the RNAP core (comprising the α1, α2, β, β′ and ω subunits), one gene (designated rpoD) encoding the major sigma factor σ 70, and a unique gene (FTL_0851) encoding a putative alternative sigma factor homologue of the σ 32 heat-shock family (designated rpoH). Hence, F. tularensis represents one of the minority of bacterial species that possess only one or no alternative sigma factor in addition to the main factor σ 70. In the present work, we show that FTL_0851 encodes a genuine σ 32 factor. Transcriptomic analyses of the F. tularensis LVS heat-stress response allowed the identification of a series of orthologues of known heat-shock genes (including those for Hsp40, GroEL, GroES, DnaK, DnaJ, GrpE, ClpB and ClpP) and a number of genes implicated in Francisella virulence. A bioinformatic analysis was used to identify genes preceded by a putative σ 32-binding site, revealing both similarities to and differences from RpoH-mediated gene expression in Escherichia coli. Our results suggest that RpoH is an essential protein of F. tularensis, and positively regulates a subset of genes involved in the heat-shock response., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.029058-0