Selective silencing of foreign DNA with low GC content by the H-NS protein in Salmonella

Science. 2006 Jul 14;313 (5784):236-238

Abstract

Bacteria can acquire foreign DNA, which called horizontal gene transfer. Foreign DNA acquired by horizontal gene transfer should be regulated under an existing cellular regulation network, or the uncontrollable expression of foreign DNA could be detrimental to the host. Previous findings suggested that nucleoid-associated protein, H-NS, can bind to curved DNA and play an inhibitory effect on gene expression. Here the authors tried to demonstrate that H-NS serves as a silencer which can recognize the genome loci with low GC content and repress their expression in Salmonella. DNA microarray was used to examine the expression difference between wild-type strain and hns mutant. GC content of H-NS-repressed loci was 48.6%, while the average was 52.2%. Chromatin immunoprecipitation followed by microarray (ChIp-on-chip) was also used to demonstrate that H-NS prefers to bind to the low GC region of the chromosome. To test if H-NS can target AT-rich DNA from a foreign source, a gene from Helicobacter pylori (GC content = 39.7%) was introduced into a nonessential region in Salmonella chromosome. Q-PCR/ChIP revealed that H-NS can significantly bind to the H. pylori DNA, and RT-PCR further confirmed that H-NS can repress the expression of the foreign DNA in Salmonella. Thus by recognizing GC/AT ratio, bacteria can use H-NS to defend against the uncontrollable expression from foreign DNA in order to prevent the detrimental effect.

References

1.   Dorman, C. J. 2004. H-NS: a universal regulator for a dynamic genome. Nat Rev Microbiol 2:391-400.

2.   Navarre, W. W., S. Porwollik, Y. Wang, M. McClelland, H. Rosen, S. J. Libby, and F. C. Fang. 2006. Selective silencing of foreign DNA with low GC content by the H-NS protein in Salmonella. Science 313:236-238.