H-NS mediates the silencing of laterally acquired genes in bacteria.
Histone-like nucleoid structuring protein (H-NS) is a modular protein that is associated with the bacterial nucleoid. We used chromatin immunoprecipitation to determine the binding sites of H-NS and RNA polymerase on the Salmonella enterica serovar Typhimurium chromosome. We found that H-NS does not bind to actively transcribed genes and does not co-localize with RNA polymerase. This shows that H-NS principally silences gene expression by restricting the access of RNA polymerase to the DNA. H-NS had previously been shown to preferentially bind to curved DNA in vitro. In fact, at the genomic level we discovered that the level of H-NS binding correlates better with the AT-content of DNA. This is likely to have evolutionary consequences because we show that H-NS binds to many Salmonella genes acquired by lateral gene transfer, and functions as a gene silencer. The removal of H-NS from the cell causes un-controlled expression of several Salmonella pathogenicity islands, and we demonstrate that this has deleterious consequences for bacterial fitness. Our discovery of this novel role for H-NS may have implications for the acquisition of foreign genes by enteric bacteria.
Lucchini
Sacha
S
Molecular Microbiology Group, Institute of Food Research, Colney, Norwich, United Kingdom.
Rowley
Gary
G
Goldberg
Martin D
MD
Hurd
Douglas
D
Harrison
Marcus
M
Hinton
Jay C D
JC
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D005075:Biological Evolution; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D022761:Gene Transfer, Horizontal; D019779:Salmonella enterica / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D012321:DNA-Directed RNA Polymerases