Bacterial Nucleoid-Associated Protein Uncouples Transcription Levels from Transcription Timing Zwir Nawrocki, Jorge Sergio Igor Yeo, Won-Sik Shin, Dongwoo Latifi, Tammy Huang, Henry Groisman, Eduardo A. Salmonella Protein domains Gene expression The histone-like nucleoid-structuring (H-NS) protein binds to horizontally acquired genes in the bacterium Salmonella enterica serovar Typhimurium, silencing their expression. We now report that overcoming the silencing effects of H-NS imposes a delay in the expression of genes activated by the transcriptional regulator PhoP. We determine that PhoP-activated genes ancestral to Salmonella are expressed before those acquired horizontally. This expression timing reflects the in vivo occupancy of the corresponding promoters by the PhoP protein. These results are surprising because some of these horizontally acquired genes reached higher mRNA levels than ancestral genes expressed earlier and were transcribed from promoters harboring PhoP-binding sites with higher in vitro affinity for the PhoP protein. Our findings challenge the often-made assumption that for genes coregulated by a given transcription factor, early genes are transcribed to higher mRNA levels than those transcribed at later times. Moreover, they provide a singular example of how gene ancestry can impact expression timing. 2015-03-18T14:11:41Z 2015-03-18T14:11:41Z 2014 info:eu-repo/semantics/article Zwir, I.; et al. Bacterial Nucleoid-Associated Protein Uncouples Transcription Levels from Transcription Timing. mBio, 5(5): e01485 (2014). [http://hdl.handle.net/10481/35300] 2150-7511 http://hdl.handle.net/10481/35300 10.1128/mBio.01485-14 eng http://creativecommons.org/licenses/by-nc-nd/3.0/ info:eu-repo/semantics/openAccess Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License American Academy of Microbiology