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Role of global and local topology in the regulation of gene expression in Streptococcus pneumoniae.

ABSTRACT: The most basic level of transcription regulation in Streptococcus pneumoniae is the organization of its chromosome in topological domains. In response to drugs that caused DNA-relaxation, a global transcriptional response was observed. Several chromosomal domains were identified based on the transcriptional response of their genes: up-regulated (U), down-regulated (D), non-regulated (N), and flanking (F). We show that these distinct domains have different expression and conservation characteristics. Microarray fluorescence units under non-relaxation conditions were used as a measure of gene transcriptional level. Fluorescence units were significantly lower in F genes than in the other domains with a similar AT content. The transcriptional level of the domains categorized them was D>U>F. In addition, a comparison of 12 S. pneumoniae genome sequences showed a conservation of gene composition within U and D domains, and an extensive gene interchange in F domains. We tested the organization of chromosomal domains by measuring the relaxation-mediated transcription of eight insertions of a heterologous Ptccat cassette, two in each type of domain, showing that transcription depended on their chromosomal location. Moreover, transcription from the four promoters directing the five genes involved in supercoiling homeostasis, located either in U (gyrB), D (topA), or N (gyrA and parEC) domains was analyzed both in their chromosomal locations and in a replicating plasmid. Although expression from the chromosomal PgyrB and PtopA showed the expected domain regulation, their expression was down-regulated in the plasmid, which behaved as a D domain. However, both PparE and PgyrA carried their own regulatory signals, their topology-dependent expression being equivalent in the plasmid or in the chromosome. In PgyrA a DNA bend acted as a DNA supercoiling sensor. These results revealed that DNA topology functions as a general transcriptional regulator, superimposed upon other more specific regulatory mechanisms.

SUBMITTER: Ferrandiz MJ

PROVIDER: S-EPMC4096756 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Role of global and local topology in the regulation of gene expression in Streptococcus pneumoniae.

Ferrándiz María-José MJ Arnanz Cristina C Martín-Galiano Antonio J AJ Rodríguez-Martín Carlos C de la Campa Adela G AG

PloS one 20140714 7

The most basic level of transcription regulation in Streptococcus pneumoniae is the organization of its chromosome in topological domains. In response to drugs that caused DNA-relaxation, a global transcriptional response was observed. Several chromosomal domains were identified based on the transcriptional response of their genes: up-regulated (U), down-regulated (D), non-regulated (N), and flanking (F). We show that these distinct domains have different expression and conservation characterist ...[more]

PMID: 25019515

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Project description:The bacterial chromosome is compacted in a manner optimal for DNA transactions to occur. The degree of compaction results from the level of DNA-supercoiling and the presence of nucleoid-binding proteins. DNA-supercoiling is homeostatically maintained by the opposing activities of relaxing DNA topoisomerases and negative supercoil-inducing DNA gyrase. DNA-supercoiling acts as a general cis regulator of transcription, which can be superimposed upon other types of more specific trans regulatory mechanism. Transcriptomic studies on the human pathogen Streptococcus pneumoniae, which has a relatively small genome (∼2 Mb) and few nucleoid-binding proteins, have been performed under conditions of local and global changes in supercoiling. The response to local changes induced by fluoroquinolone antibiotics, which target DNA gyrase subunit A and/or topoisomerase IV, involves an increase in oxygen radicals which reduces cell viability, while the induction of global supercoiling changes by novobiocin (a DNA gyrase subunit B inhibitor), or by seconeolitsine (a topoisomerase I inhibitor), has revealed the existence of topological domains that specifically respond to such changes. The control of DNA-supercoiling in S. pneumoniae occurs mainly via the regulation of topoisomerase gene transcription: relaxation triggers the up-regulation of gyrase and the down-regulation of topoisomerases I and IV, while hypernegative supercoiling down-regulates the expression of topoisomerase I. Relaxation affects 13% of the genome, with the majority of the genes affected located in 15 domains. Hypernegative supercoiling affects 10% of the genome, with one quarter of the genes affected located in 12 domains. However, all the above domains overlap, suggesting that the chromosome is organized into topological domains with fixed locations. Based on its response to relaxation, the pneumococcal chromosome can be said to be organized into five types of domain: up-regulated, down-regulated, position-conserved non-regulated, position-variable non-regulated, and AT-rich. The AT content is higher in the up-regulated than in the down-regulated domains. Genes within the different domains share structural and functional characteristics. It would seem that a topology-driven selection pressure has defined the chromosomal location of the metabolism, virulence and competence genes, which suggests the existence of topological rules that aim to improve bacterial fitness.

Project description:Previous studies have indicated that PsaR of Streptococcus pneumoniae is a manganese-dependent regulator, negatively affecting the expression of at least seven genes. Here, we extended these observations by transcriptome and proteome analysis of psaR mutants in strains D39 and TIGR4. The microarray analysis identified three shared PsaR targets: the psa-operon, pcpA, and prtA. Additionally, we found 31 genes to be regulated by PsaR in D39 only, most strikingly a cellobiose-specific PTS and a putative bacteriocin operon (sp0141-sp0146). In TIGR4, 14 PsaR gene targets were detected, with the rlrA pathogenicity islet being the most pronounced. Proteomics confirmed most of the shared gene targets. To examine the contribution of PsaR to pneumococcal virulence, we compared D39 and TIGR4 wild-type (wt) and psaR-mutants in three murine infection models. During colonization, no clear effect was observed of the psaR mutation in either D39 or TIGR4. In the pneumonia model, small but significant differences were observed in the lungs of mice infected with either D39wt or âpsaR: D39âpsaR had an initial advantage in survival in the lungs. Conversely, TIGR4âpsaR-infected mice had significantly lower bacterial loads at 24h only. Finally, during experimental bacteremia, D39âpsaR-infected mice had significantly lower bacterial loads in the blood stream than wt-infected mice for the first 24h of infection. TIGR4âpsaR showed attenuation at 36h only. In conclusion, our results show that PsaR of D39 and TIGR4 has a strain-specific role in global gene expression and in the development of bacteremia in mice. Microarray analysis was performed essentially as described (Hendriksen et al., 2007; Hendriksen et al., 2008a). In short, 500 ml of CDM was inoculated with 10-20 colonies from agar plates, and these cultures were statically grown at 37Â°C. Samples for RNA isolation were taken when the cultures reached an optical density (OD600) of 0.2 (mid-log growth). RNA was isolated and purified using the High Pure RNA isolation kit (Roche diagnostics) as described (Hendriksen et al., 2007; Hendriksen et al., 2008a). Contaminating genomic DNA was removed by treatment with RNase-free DNase I (Roche diagnostics). RNA was isolated from three replicate cultures. Synthesis, subsequent labeling of cDNA, and microarray hybridization was performed as described (Hendriksen et al., 2007; Kloosterman et al., 2006). In all cases, dye-swapping was performed with one of the three biological replicates. Microarrays used in this study were constructed as described (Hendriksen et al., 2007; Kloosterman et al., 2006) and contain amplicons representing 2,087 ORFs of S. pneumoniae TIGR4 and 184 ORFs unique for S. pneumoniae R6, all spotted in duplicate.

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Role of global and local topology in the regulation of gene expression in Streptococcus pneumoniae.

Publications

Role of global and local topology in the regulation of gene expression in Streptococcus pneumoniae.

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