H-NS, the genome sentinel

Dorman, Charles J.

doi:10.1038/nrmicro1598

Cited by 323 publications

(314 citation statements)

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“…The horizontal transfer of complete genes raises the important issue of how the expression of these genes is regulated in the new host. H-NS protein, a pleiotropic repressor of transcription, has a key role in selective silencing of the transcription of large numbers of horizontally acquired AT-rich genes, including pathogenicity islands (Dorman, 2007). It was recently found that Rho termination is required to suppress similar silencing (Cardinale et al, 2008).…”

Section: Discussionmentioning

confidence: 99%

Genomic comparison of Bradyrhizobium japonicum strains with different symbiotic nitrogen-fixing capabilities and other Bradyrhizobiaceae members

et al. 2008

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Comparative genomic hybridization (CGH) was performed with nine strains of Bradyrhizobium japonicum (a symbiotic nitrogen-fixing bacterium associated with soybean) and eight other members of the Bradyrhizobiaceae by DNA macroarray of B. japonicum USDA110. CGH clearly discriminated genomic variations in B. japonicum strains, but similar CGH patterns were observed in other members of the Bradyrhizobiaceae. The most variable regions were 14 genomic islands (4-97 kb) and low G þ C regions on the USDA110 genome, some of which were missing in several strains of B. japonicum and other members of the Bradyrhizobiaceae. The CGH profiles of B. japonicum were classified into three genome types: 110, 122 and 6. Analysis of DNA sequences around the boundary regions showed that at least seven genomic islands were missing in genome type 122 as compared with type 110. Phylogenetic analysis for internal transcribed sequences revealed that strains belonging to genome types 110 and 122 formed separate clades. Thus genomic islands were horizontally inserted into the ancestor genome of type 110 after divergence of the type 110 and 122 strains. To search for functional relationships of variable genomic islands, we conducted linear models of the correlation between the existence of genomic regions and the parameters associated with symbiotic nitrogen fixation in soybean. Variable genomic regions including genomic islands were associated with the enhancement of symbiotic nitrogen fixation in B. japonicum USDA110.

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Section: Discussionmentioning

confidence: 99%

Genomic comparison of Bradyrhizobium japonicum strains with different symbiotic nitrogen-fixing capabilities and other Bradyrhizobiaceae members

et al. 2008

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“…Both functions are compatible with the structures assumed by plectonemically coiled DNA superhelices. Although in a plectoneme H-NS can bridge the two component duplexes, the binding of the protein is nucleated on one strand by an A/T-rich sequence (Bouffartigues et al 2007;Lang et al 2007;Dorman 2007). H-NS binding can then spread to adjacent regions of similar base composition, forming a nucleofilament.…”

Section: H-ns Nucleoprotein Complexesmentioning

confidence: 99%

The regulatory role of DNA supercoiling in nucleoprotein complex assembly and genetic activity

Muskhelishvili

Travers

2016

Biophys Rev

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We argue that dynamic changes in DNA supercoiling in vivo determine both how DNA is packaged and how it is accessed for transcription and for other manipulations such as recombination. In both bacteria and eukaryotes, the principal generators of DNA superhelicity are DNA translocases, supplemented in bacteria by DNA gyrase. By generating gradients of superhelicity upstream and downstream of their site of activity, translocases enable the differential binding of proteins which preferentially interact with respectively more untwisted or more writhed DNA. Such preferences enable, in principle, the sequential binding of different classes of protein and so constitute an essential driver of chromatin organization.Keywords DNA supercoiling . DNA translocases . Chromatin organization . Superhelicity gradients . DNA untwisting . DNAwrithing Dynamic changes of DNA supercoiling act as a driving force behind the alterations of genetic activity and DNA compaction both in eukaryotes and prokaryotes. Both these processes involve formation of spatially organized nucleoprotein structures by DNA architectural proteins. Whereas in eukaryotes the paradigmal example is the histone octamer, in prokaryotes a similar function is attributed to a small class of highly abundant nucleoid-associated proteins. We argue that, depending on the primary sequence organization, the changes of superhelicity elicit various alterations of local DNA geometry, while these, in turn, facilitate the assembly of distinct nucleoprotein structures pertinent to genetic function. Genome-wide conversion of the superhelical energy into various three-dimensional DNA structures thus acts as an analogue code coordinating the energy supply with the genetic expression of the chromosome.Recent studies make it increasingly clear that the DNA double helix carries at least two types of encoded information and that these include the well-known genetic code and the structural information determining the form and physical properties of the double helix itself. Since both these information types are inscribed in the same DNA sequence, and yet one is discrete whereas the other is continuous, they have been respectively dubbed the digital and analog DNA codes (Marr et al. 2008;Travers et al. 2012;Muskhelishvili and Travers 2013). The potential of the DNA to adopt distinct configurations is strongly modulated by DNA supercoiling, which is increasingly recognized as one of the major forces coordinating the cellular DNA transactions in both prokaryotes (including Archaea) and eukaryotes.DNA supercoiling can be generated by the simple application of torque to the double helix (Strick et al. 1998) but, importantly, because the DNA molecule itself possesses chirality-it is, after all, a right-handed double helix-the local structures stabilized by changes in superhelical density depend on both the sign and strength of the applied torque. For example, both positive and negative torque (respectively overand underwinding of the double helix) can change the intrinsic coiling of ...

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“…H-NS has long been regarded as a global modulator of gene expression in response to pH, temperature, osmolarity and growth phase [14][15][16]. A large proportion of Salmonella genes induced upon temperature shift from 25°C to 37°C are dependent on H-NS [17], an effect attributed to putative conformational changes in H-NS and reduced DNA binding.…”

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confidence: 99%

New insights into transcriptional regulation by H-NS

Fang

Rimsky

2008

Current Opinion in Microbiology

188

173

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H-NS, a nucleoid-associated DNA-binding protein of enteric bacteria, was discovered thirty-five years ago and subsequently found to exert widespread and highly pleiotropic effects on gene regulation. H-NS binds to high-affinity sites and spreads along adjacent AT-rich DNA to silence transcription. Preferential binding to sequences with higher AT-content than the resident genome allows H-NS to repress the expression of foreign DNA in a process known as "xenogeneic silencing." Counter-silencing by a variety of mechanisms facilitates the evolutionary acquisition of horizontally transferred genes and their integration into pre-existing regulatory networks. This review will highlight recent insights into the mechanism and biological importance of H-NS-DNA interactions. H-NS--A Nucleoid ProteinH-NS is an abundant DNA-binding protein implicated in the organization of the bacterial chromosome [1]. H-NS and other nucleoid-associated proteins can affect DNA topology at specific loci, thereby modulating gene transcription. Binding by these proteins is proposed to selectively direct supercoiling effects to promoters [2•]. Mutation of hns alters the responsiveness of transcription to changes in DNA superhelicity. Regulatory effects of supercoiling are linked to metabolic and environmental conditions. Thus, H-NS has been viewed as a nucleoid structuring protein with global effects on gene expression [3].H-NS exists primarily as a dimer at low concentrations but can multimerize into higher order complexes [4,5] that form bridges between adjacent DNA helices [6]. Optical tweezers have been used to demonstrate that H-NS dimers or multimers can simultaneously interact with separate DNA binding sites [7••]. H-NS-coated DNA is not self-interactive, suggesting that dimerization or oligomerization must precede DNA binding for bridging to occur. Force measurements suggest that transcription barriers created by H-NS binding are weak (∼7 pN) and readily overcome, so that H-NS oligomers pose only a relative barrier to translocating RNA polymerase. DNA bridging is a conserved feature of H-NS homologs found in most gram-negative bacteria [8] that appears to constrain large DNA loops [9••] and helps to account for the effects of H-NS on transcription. However, it must be noted that the relationship between bridging as a general effect and the silencing of specific promoters is not yet clear.H-NS is more appropriately viewed as a determinant of chromosomal architecture rather than as a general structural component. The analysis of nucleoids treated with urea suggests that *Corresponding Author : Tel 206-275-0966, Fax 206-616-1575, e-mail : fcfang@u.washington.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production proce...

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H-NS, the genome sentinel

Cited by 323 publications

References 85 publications

Genomic comparison of Bradyrhizobium japonicum strains with different symbiotic nitrogen-fixing capabilities and other Bradyrhizobiaceae members

Genomic comparison of Bradyrhizobium japonicum strains with different symbiotic nitrogen-fixing capabilities and other Bradyrhizobiaceae members

The regulatory role of DNA supercoiling in nucleoprotein complex assembly and genetic activity

New insights into transcriptional regulation by H-NS

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