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Genome‐wide analysis of the H‐NS and Sfh regulatory networks in Salmonella Typhimurium identifies a plasmid‐encoded transcription silencing mechanism
Author(s) -
Dillon Shane C.,
Cameron Andrew D. S.,
Hokamp Karsten,
Lucchini Sacha,
Hinton Jay C. D.,
Dorman Charles J.
Publication year - 2010
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2010.07173.x
Subject(s) - biology , plasmid , shigella flexneri , genetics , salmonella enterica , genome , gene , population , chromatin , chromatin immunoprecipitation , transcription (linguistics) , repressor , dna , transcription factor , promoter , escherichia coli , gene expression , demography , sociology , linguistics , philosophy
Summary The conjugative IncHI1 plasmid pSfR27 from Shigella flexneri 2a strain 2457T encodes the Sfh protein, a paralogue of the global transcriptional repressor H‐NS. Sfh allows pSfR27 to be transmitted to new bacterial hosts with minimal impact on host fitness, providing a ‘stealth’ function whose molecular mechanism has yet to be determined. The impact of the Sfh protein on the Salmonella enterica serovar Typhimurium transcriptome was assessed and binding sites for Sfh in the Salmonella Typhimurium genome were identified by chromatin immunoprecipitation. Sfh did not bind uniquely to any sites. Instead, it bound to a subset of the larger H‐NS regulatory network. Analysis of Sfh binding in the absence of H‐NS revealed a greatly expanded population of Sfh binding sites that included the majority of H‐NS target genes. Furthermore, the presence of plasmid pSfR27 caused a decrease in H‐NS interactions with the S. Typhimurium chromosome, suggesting that the A + T‐rich DNA of this large plasmid acts to titrate H‐NS, removing it from chromosomal locations. It is proposed that Sfh acts as a molecular backup for H‐NS and that it provides its ‘stealth’ function by replacing H‐NS on the chromosome, thus minimizing disturbances to the H‐NS‐DNA binding pattern in cells that acquire pSfR27.