Figueroa Bossi, NaraSánchez Romero, María AntoniaKerboriou, PatriciaNaquin, DelphineMendes, ClaraBouloc, PhilippeCasadesus Pursals, JosepBossi, Lionello2023-05-302023-05-302022Figueroa Bossi, N., Sánchez Romero, M.A., Kerboriou, P., Naquin, D., Mendes, C., Bouloc, P.,...,Bossi, L. (2022). Pervasive transcription enhances the accessibility of H-NS–silenced promoters and generates bistability in Salmonella virulence gene expression. Proceedings of the National Academy of Sciences (PNAS), 119 (30), e2203011119. https://doi.org/10.1073/pnas.2203011119.0027-84241091-6490https://hdl.handle.net/11441/146778In Escherichia coli and Salmonella, many genes silenced by the nucleoid structuring protein H-NS are activated upon inhibiting Rho-dependent transcription termination. This response is poorly understood and difficult to reconcile with the view that H-NS acts mainly by blocking transcription initiation. Here we have analyzed the basis for the up-regulation of H-NS–silenced Salmonella pathogenicity island 1 (SPI-1) in cells depleted of Rho-cofactor NusG. Evidence from genetic experiments, semiquantitative 50 rapid amplification of complementary DNA ends sequencing (5’ RACE-Seq), and chromatin immunoprecipitation sequencing (ChIP-Seq) shows that transcription originating from spurious antisense promoters, when not stopped by Rho, elongates into a H-NS–bound regulatory region of SPI-1, displacing H-NS and rendering the DNA accessible to the master regulator HilD. In turn, HilD’s ability to activate its own transcription triggers a positive feedback loop that results in transcriptional activation of the entire SPI-1. Significantly, single-cell analyses revealed that this mechanism is largely responsible for the coexistence of two subpopulations of cells that either express or do not express SPI-1 genes. We propose that cell-to-cell differences produced by stochastic spurious transcription, combined with feedback loops that perpetuate the activated state, can generate bimodal gene expression patterns in bacterial populations.application/pdf9 p.engAttribution-NonCommercial-NoDerivatives 4.0 Internacionalhttp://creativecommons.org/licenses/by-nc-nd/4.0/pervasive transcriptionH-NSsilencingpathogenicity islandsbistabilityinfo:eu-repo/semantics/articleinfo:eu-repo/semantics/openAccesshttps://doi.org/10.1073/pnas.2203011119