A New Noncoding RNA Arranges Bacterial Chromosome Organization

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Nucleic Acids Research, 2006

The Escherichia coli chromosome is condensed into an ill-defined structure known as the nucleoid. Nucleoid-associated DNA-binding proteins are involved in maintaining this structure and in mediating chromosome compaction. We have exploited chromatin immunoprecipitation and high-density microarrays to study the binding of three such proteins, FIS, H-NS and IHF, across the E.coli genome in vivo. Our results show that the distribution of these proteins is biased to intergenic parts of the genome, and that the binding profiles overlap. Hence some targets are associated with combinations of bound FIS, H-NS and IHF. In addition, many regions associated with FIS and H-NS are also associated with RNA polymerase.

BMC Microbiology, 2016

Background: It is unclear how DNA is packaged in a bacterial cell in the absence of nucleosomes. To investigate the initial level of DNA condensation in bacterial nucleoid we used in vivo DNA digestion coupled with high-throughput sequencing of the digestion-resistant fragments. To this end, we transformed E. coli cells with a plasmid expressing micrococcal nuclease. The nuclease expression was under the control of AraC repressor, which enabled us to perform an inducible digestion of bacterial nucleoid inside a living cell. Results: Analysis of the genomic localization of the digestion-resistant fragments revealed their non-random distribution. The patterns observed in the distribution of the sequenced fragments indicate the presence of short DNA segments protected from the enzyme digestion, possibly because of interaction with DNA-binding proteins. The average length of such digestion-resistant segments is about 50 bp and the characteristic repeat in their distribution is about 90 bp. The gene starts are depleted of the digestion-resistant fragments, suggesting that these genomic regions are more exposed than genomic sequences on average. Sequence analysis of the digestion-resistant segments showed that while the GC-content of such sequences is close to the genome-wide value, they are depleted of A-tracts as compared to the bulk genomic DNA or to the randomized sequence of the same nucleotide composition. Conclusions: Our results suggest that DNA is packaged in the bacterial nucleoid in a non-random way that facilitates interaction of the DNA binding factors with regulatory regions of the genome.

BMC genomics, 2006

Mobile elements are involved in genomic rearrangements and virulence acquisition, and hence, are important elements in bacterial genome evolution. The insertion of some specific Insertion Sequences had been associated with repetitive extragenic palindromic (REP) elements. Considering that there are a sufficient number of available genomes with described REPs, and exploiting the advantage of the traceability of transposition events in genomes, we decided to exhaustively analyze the relationship between REP sequences and mobile elements. This global multigenome study highlights the importance of repetitive extragenic palindromic elements as target sequences for transposases. The study is based on the analysis of the DNA regions surrounding the 981 instances of Insertion Sequence elements with respect to the positioning of REP sequences in the 19 available annotated microbial genomes corresponding to species of bacteria with reported REP sequences. This analysis has allowed the detecti...

Nature, 2009

Estimates of the total number of bacterial species 1-3 indicate that existing DNA sequence databases carry only a tiny fraction of the total amount of DNA sequence space represented by this division of life. Indeed, environmental DNA samples have been shown to encode many previously unknown classes of proteins 4 and RNAs 5 . Bioinformatics searches 6-10 of genomic DNA from bacteria commonly identify new noncoding RNAs (ncRNAs) 10-12 such as riboswitches 13,14 . In rare instances, RNAs that exhibit more extensive sequence and structural conservation across a wide range of bacteria are encountered . Given that large structured RNAs are known to carry out complex biochemical functions such as protein synthesis and RNA processing reactions, identifying more RNAs of great size and intricate structure is likely to reveal additional biochemical functions that can be achieved by RNA. We applied an updated computational pipeline 17 to discover ncRNAs that rival the known large ribozymes in size and structural complexity or that are among the most abundant RNAs in bacteria that encode them. These RNAs would have been difficult or impossible to detect without examining environmental DNA sequences, indicating that numerous RNAs with extraordinary size, structural complexity, or other exceptional characteristics remain to be discovered in unexplored sequence space.

Journal of Molecular Biology, 2012

Nucleic Acids Research, 2012

Extragenic sequences in genomes, such as microRNA and CRISPR, are vital players in the cell. Repetitive extragenic palindromic sequences (REPs) are a class of extragenic sequences, which form nucleotide stem-loop structures. REPs are found in many bacterial species at a high copy number and are important in regulation of certain bacterial functions, such as Integration Host Factor recruitment and mRNA turnover. Although a new clade of putative transposases (RAYTs or TnpA REP ) is often associated with an increase in these repeats, it is not clear how these proteins might have directed amplification of REPs. We report here the structure to 2.6 Å of TnpA REP from Escherichia coli MG1655 bound to a REP. Sequence analysis showed that TnpA REP is highly related to the IS200/IS605 family, but in contrast to IS200/IS605 transposases, TnpA REP is a monomer, is auto-inhibited and is active only in manganese. These features suggest that, relative to IS200/IS605 transposases, it has evolved a different mechanism for the movement of discrete segments of DNA and has been severely down-regulated, perhaps to prevent REPs from sweeping through genomes.

PLOS Genetics, 2019

How genomes are organized within cells and how the 3D architecture of a genome influences cellular functions are significant questions in biology. A bacterial genomic DNA resides inside cells in a highly condensed and functionally organized form called nucleoid (nucleus-like structure without a nuclear membrane). The Escherichia coli chromosome or nucleoid is composed of the genomic DNA, RNA, and protein. The nucleoid forms by condensation and functional arrangement of a single chromosomal DNA with the help of chromosomal architectural proteins and RNA molecules as well as DNA supercoiling. Although a high-resolution structure of a bacterial nucleoid is yet to come, five decades of research has established the following salient features of the E. coli nucleoid elaborated below: 1) The chromosomal DNA is on the average a negatively supercoiled molecule that is folded as plectonemic loops, which are confined into many independent topological domains due to supercoiling diffusion barriers; 2) The loops spatially organize into megabase size regions called macrodomains, which are defined by more frequent physical interactions among DNA sites within the same macrodomain than between different macrodomains; 3) The condensed and spatially organized DNA takes the form of a helical ellipsoid radially confined in the cell; and 4) The DNA in the chromosome appears to have a condition-dependent 3-D structure that is linked to gene expression so that the nucleoid architecture and gene transcription are tightly interdependent, influencing each other reciprocally. Current advents of high-resolution microscopy, single-molecule analysis and molecular structure determination of the components are expected to reveal the total structure and function of the bacterial nucleoid.

Biochimica et biophysica acta, 2012

In contrast to organized hierarchical structure of eukaryotic chromosome, bacterial chromosomes are believed not to have such structures. The genomes of bacteria are condensed into a compact structure called the nucleoid. Among many architectural, histone-like proteins which associate with the chromosomal DNA is HU which is implicated in folding DNA into a compact structure by bending and wrapping DNA. Unlike the majority of other histone-like proteins, HU is highly conserved in eubacteria and unique in its ability to bind RNA. Furthermore, an HU mutation profoundly alters the cellular transcription profile and consequently has global effects on physiology and the lifestyle of E. coli. Here we provide a short overview of the mechanisms by which the nucleoid is organized into different topological domains. We propose that HU is a major player in creating domain-specific superhelicities and thus influences the transcription profile from the constituent promoters. This article is part of a Special Issue entitled: Chromatin in time and space.

Genetics, 2001

Spontaneous deletion mutations often occur at short direct repeats that flank inverted repeat sequences. Inverted repeats may initiate genetic rearrangements by formation of hairpin secondary structures that block DNA polymerases or are processed by structure-specific endonucleases. We have investigated the ability of inverted repeat sequences to stimulate deletion of flanking direct repeats in Escherichia coli. Propensity for cruciform extrusion in duplex DNA correlated with stimulation of flanking deletion, which was partially sbcD dependent. We propose two mechanisms for palindrome-stimulated deletion, SbcCD dependent and SbcCD independent. The SbcCD-dependent mechanism is initiated by SbcCD cleavage of cruciforms in duplex DNA followed by RecA-independent single-strand annealing at the flanking direct repeats, generating a deletion. Analysis of deletion endpoints is consistent with this model. We propose that the SbcCD-independent pathway involves replication slipped mispairing,...