Nucleoid-associated proteins (NAPs) play a central role in chromosome organization and environment-responsive transcription regulation. The Bacillus subtilis-encoded NAP Rok binds preferentially AT... Show moreNucleoid-associated proteins (NAPs) play a central role in chromosome organization and environment-responsive transcription regulation. The Bacillus subtilis-encoded NAP Rok binds preferentially AT-rich regions of the genome, which often contain genes of foreign origin that are silenced by Rok binding. Additionally, Rok plays a role in chromosome architecture by binding in genomic clusters and promoting chromosomal loop formation. Based on this, Rok was proposed to be a functional homolog of E. coli H-NS. However, it is largely unclear how Rok binds DNA, how it represses transcription and whether Rok mediates environment-responsive gene regulation. Here, we investigated Rok's DNA binding properties and the effects of physico-chemical conditions thereon. We demonstrate that Rok is a DNA bridging protein similar to prototypical H-NS-like proteins. However, unlike these proteins, the DNA bridging ability of Rok is not affected by changes in physico-chemical conditions. The DNA binding properties of the Rok interaction partner sRok are affected by salt concentration. This suggests that in a minority of Bacillus strains Rok activity can be modulated by sRok, and thus respond indirectly to environmental stimuli. Despite several functional similarities, the absence of a direct response to physico-chemical changes establishes Rok as disparate member of the H-NS family. Show less
Du, C.; Willemse, J.J.; Erkelens, A.M.; Carrion Bravo, V.J.; Dame, R.T.; Wezel, G.P. van 2022
Bacterial chromosome structure is, to a great extent, organized by a diverse group of proteins collectively referred to as nucleoid-associated proteins (NAPs). Many NAPs have been well studied in... Show moreBacterial chromosome structure is, to a great extent, organized by a diverse group of proteins collectively referred to as nucleoid-associated proteins (NAPs). Many NAPs have been well studied in Streptomyces, including Lsr2, HupA, HupS, and sIHF. Here, we show that SCO1839 represents a novel family of Actinobacteria NAPs and recognizes a consensus sequence consisting of GATC followed by (A/T)T. The protein, which is expressed in particular during sporulation, was designated Gbn for GATC-binding NAP. Deletion of gbn led to alterations in development and antibiotic production in Streptomyces coelicolor. Chromatin immunoprecipitation sequencing (ChIP-Seq) detected more than 2,800 binding regions, encompassing around 3,600 GATCWT motifs. This amounts to 55% of all such sequences in the S. coelicolor genome. DNA binding of Gbn in vitro minimally changes DNA conformation, suggesting a modest role in chromosome organization only, in addition to a gene regulatory role. Transcriptomics analysis showed that Gbn binding generally leads to reduced gene expression. The DNA binding profiles were nearly identical between vegetative and aerial growth. Exceptions are SCO1311 and SCOt32, for a tRNA editing enzyme and a tRNA that recognizes the rare leucine codon CUA, respectively, which nearly exclusively bound during vegetative growth. Taken together, our data show that Gbn is a highly pleiotropic NAP that impacts growth and development in streptomycetes.IMPORTANCE A large part of the chemical space of bioactive natural products is derived from Actinobacteria. Many of the biosynthetic gene clusters for these compounds are cryptic; in others words, they are expressed in nature but not in the laboratory. Understanding the global regulatory networks that control gene expression is key to the development of approaches to activate this biosynthetic potential. Chromosome structure has a major impact on the control of gene expression in eukaryotes. In bacteria, the organization of chromosome structure is mediated by multiple factors, including macromolecular biophysics processes, biological processes, and, more importantly, a diverse group of proteins referred to collectively as nucleoid-associated proteins (NAPs). We here present the discovery of a novel and extremely pleiotropic NAP, which we refer to as Gbn. Gbn is an Actinobacteria-specific protein that binds to GATC sequences, with a subtle but broad effect on global gene expression, especially during the late developmental stage. The discovery of Gbn is a new step toward better understanding of how gene expression and chromosome structure are governed in antibiotic-producing streptomycetes. Show less
Bacteria use specific silencing proteins to prevent spurious transcription of horizontally acquired DNA. Here, Forrest et al. describe differences in silencing strategies between E. coli and... Show moreBacteria use specific silencing proteins to prevent spurious transcription of horizontally acquired DNA. Here, Forrest et al. describe differences in silencing strategies between E. coli and Bacillus subtilis, driven by the respective specificities of the silencing protein and the RNA polymerase in each organism.Horizontal gene transfer facilitates dissemination of favourable traits among bacteria. However, foreign DNA can also reduce host fitness: incoming sequences with a higher AT content than the host genome can misdirect transcription. Xenogeneic silencing proteins counteract this by modulating RNA polymerase binding. In this work, we compare xenogeneic silencing strategies of two distantly related model organisms: Escherichia coli and Bacillus subtilis. In E. coli, silencing is mediated by the H-NS protein that binds extensively across horizontally acquired genes. This prevents spurious non-coding transcription, mostly intragenic in origin. By contrast, binding of the B. subtilis Rok protein is more targeted and mostly silences expression of functional mRNAs. The difference reflects contrasting transcriptional promiscuity in E. coli and B. subtilis, largely attributable to housekeeping RNA polymerase sigma factors. Thus, whilst RNA polymerase specificity is key to the xenogeneic silencing strategy of B. subtilis, transcriptional promiscuity must be overcome to silence horizontally acquired DNA in E. coli. Show less
Rashid, F.Z.M.; Mahlandt, E.; Vaart, M. van der; Boer, D.E.C.; Alvarez, M.V.; Henneman, B.; ... ; Dame, R.T. 2022
The interplay between three-dimensional chromosome organisation and genomic processes such as replication and transcription necessitates in vivo studies of chromosome dynamics. Fluorescent organic... Show moreThe interplay between three-dimensional chromosome organisation and genomic processes such as replication and transcription necessitates in vivo studies of chromosome dynamics. Fluorescent organic dyes are often used for chromosome labelling in vivo. The mode of binding of these dyes to DNA cause its distortion, elongation, and partial unwinding. The structural changes induce DNA damage and interfere with the binding dynamics of chromatin-associated proteins, consequently perturbing gene expression, genome replication, and cell cycle progression. We have developed a minimally-perturbing, genetically encoded fluorescent DNA label consisting of a (photo-switchable) fluorescent protein fused to the DNA-binding domain of H-NS - a bacterial nucleoid-associated protein. We show that this DNA label, abbreviated as HI-NESS (H-NS-based indicator for nucleic acid stainings), is minimally-perturbing to genomic processes and labels chromosomes in eukaryotic cells in culture, and in zebrafish embryos with preferential binding to AT-rich chromatin. Show less
The interplay between three-dimensional chromosome organisation and genomic processes such as replication and transcription necessitates in vivo studies of chromosome dynamics. Fluorescent organic... Show moreThe interplay between three-dimensional chromosome organisation and genomic processes such as replication and transcription necessitates in vivo studies of chromosome dynamics. Fluorescent organic dyes are often used for chromosome labelling in vivo. The mode of binding of these dyes to DNA cause its distortion, elongation, and partial unwinding. The structural changes induce DNA damage and interfere with the binding dynamics of chromatin-associated proteins, consequently perturbing gene expression, genome replication, and cell cycle progression. We have developed a minimally-perturbing, genetically encoded fluorescent DNA label consisting of a (photo-switchable) fluorescent protein fused to the DNA-binding domain of H-NS - a bacterial nucleoid-associated protein. We show that this DNA label, abbreviated as HI-NESS (H-NS-based indicator for nucleic acid stainings), is minimally-perturbing to genomic processes and labels chromosomes in eukaryotic cells in culture, and in zebrafish embryos with preferential binding to AT-rich chromatin. Show less
H-NS proteins act as osmotic sensors translating changes in osmolarity into altered DNA binding properties, thus, regulating enterobacterial genome organization and genes transcription. The... Show moreH-NS proteins act as osmotic sensors translating changes in osmolarity into altered DNA binding properties, thus, regulating enterobacterial genome organization and genes transcription. The molecular mechanism underlying the switching process and its conservation among H-NS family members remains elusive. Here, we focus on the H-NS family protein MvaT from Pseudomonas aeruginosa and demonstrate experimentally that its protomer exists in two different conformations, corresponding to two different functional states. In the half-opened state (dominant at low salt) the protein forms filaments along DNA, in the fully opened state (dominant at high salt) the protein bridges DNA. This switching is a direct effect of ionic strength on electrostatic interactions between the oppositely charged DNA binding and N-terminal domains of MvaT. The asymmetric charge distribution and intramolecular interactions are conserved among the H-NS family of proteins. Therefore, our study establishes a general paradigm for the molecular mechanistic basis of the osmosensitivity of H-NS proteins. Show less
Qin, L.; Erkelens, A.M.; Ben Bdira, F.; Dame, R.T. 2019
Every organism across the tree of life compacts and organizes its genome with architectural chromatin proteins. While eukaryotes and archaea express histone proteins, the organization of bacterial... Show moreEvery organism across the tree of life compacts and organizes its genome with architectural chromatin proteins. While eukaryotes and archaea express histone proteins, the organization of bacterial chromosomes is dependent on nucleoid-associated proteins. In Escherichia coli and other proteobacteria, the histone-like nucleoid structuring protein (H-NS) acts as a global genome organizer and gene regulator. Functional analogues of H-NS have been found in other bacterial species: MvaT in Pseudomonas species, Lsr2 in actinomycetes and Rok in Bacillus species. These proteins complement hns− phenotypes and have similar DNA-binding properties, despite their lack of sequence homology. In this review, we focus on the structural and functional characteristics of these four architectural proteins. They are able to bridge DNA duplexes, which is key to genome compaction, gene regulation and their response to changing conditions in the environment. Structurally the domain organization and charge distribution of these proteins are conserved, which we suggest is at the basis of their conserved environment responsive behaviour. These observations could be used to find and validate new members of this protein family and to predict their response to environmental changes. Show less
