CRISPR Screening Uncovers a Long-Range Enhancer for ONECUT1 in Pancreatic Differentiation and Links a Diabetes Risk Variant.

Functional enhancer annotation is a valuable first step for understanding tissue-specific transcriptional regulation and prioritizing disease-associated non-coding variants for investigation. However, unbiased enhancer discovery in physiologically relevant contexts remains a major challenge. To discover regulatory elements pertinent to diabetes, we conducted a CRISPR interference (CRISPRi) screen in the human pluripotent stem cell (hPSC) pancreatic differentiation system. Among the enhancers uncovered, we focused on a long-range enhancer ∼664 kb from the ONECUT1 promoter, as coding mutations in ONECUT1 cause pancreatic hypoplasia and neonatal diabetes. Homozygous enhancer deletion in hPSCs was associated with a near-complete loss of ONECUT1 gene expression and compromised pancreatic differentiation. This enhancer contains a confidently fine-mapped type 2 diabetes (T2D) associated variant (rs528350911) which disrupts a GATA motif. Introduction of the risk variant into hPSCs revealed substantially reduced binding of key pancreatic transcription factors (GATA4, GATA6 and FOXA2) on the edited allele, accompanied by a slight reduction of ONECUT1 transcription, supporting a causal role for this risk variant in metabolic disease. This work expands our knowledge about transcriptional regulation in pancreatic development through the characterization of a long-range enhancer and highlights the utility of enhancer discovery in disease-relevant settings for understanding monogenic and complex disease.

Correction to "Carbodiimide Ring-Opening Metathesis Polymerization".

[This corrects the article DOI: 10.1021/acscentsci.3c00032.].

Discovery of Competent Chromatin Regions in Human Embryonic Stem Cells.

The mechanisms underlying the ability of embryonic stem cells (ESCs) to rapidly activate lineage-specific genes during differentiation remain largely unknown. Through multiple CRISPR-activation screens, we discovered human ESCs have pre-established transcriptionally competent chromatin regions (CCRs) that support lineage-specific gene expression at levels comparable to differentiated cells. CCRs reside in the same topological domains as their target genes. They lack typical enhancer-associated histone modifications but show enriched occupancy of pluripotent transcription factors, DNA demethylation factors, and histone deacetylases. TET1 and QSER1 protect CCRs from excessive DNA methylation, while HDAC1 family members prevent premature activation. This "push and pull" feature resembles bivalent domains at developmental gene promoters but involves distinct molecular mechanisms. Our study provides new insights into pluripotency regulation and cellular plasticity in development and disease. One sentence summary: We report a class of distal regulatory regions distinct from enhancers that confer human embryonic stem cells with the competence to rapidly activate the expression of lineage-specific genes.

Carbodiimide Ring-Opening Metathesis Polymerization.

Controlled incorporation of nitrogen into macromolecular skeletons is a long-standing challenge whose resolution would enable the preparation of soft materials with the scalability of man-made plastics and functionality of Nature's proteins. Nylons and polyurethanes notwithstanding, nitrogen-rich polymer backbones remain scarce, and their synthesis typically lacks precision. Here we report a strategy that begins to address this limitation founded on a mechanistic discovery: ring-opening metathesis polymerization (ROMP) of carbodiimides followed by carbodiimide derivatization. An iridium guanidinate complex was found to initiate and catalyze ROMP of N-aryl and N-alkyl cyclic carbodiimides. Nucleophilic addition to the resulting polycarbodiimides enabled the preparation of polyureas, polythioureas, and polyguanidinates with varied architectures. This work advances the foundations of metathesis chemistry and opens the door to systematic investigations of structure-folding-property relationships in nitrogen-rich macromolecules.

Genetic Engineering of Immune Evasive Stem Cell-Derived Islets.

Genome editing has the potential to revolutionize many investigative and therapeutic strategies in biology and medicine. In the field of regenerative medicine, one of the leading applications of genome engineering technology is the generation of immune evasive pluripotent stem cell-derived somatic cells for transplantation. In particular, as more functional and therapeutically relevant human pluripotent stem cell-derived islets (SCDI) are produced in many labs and studied in clinical trials, there is keen interest in studying the immunogenicity of these cells and modulating allogeneic and autoimmune immune responses for therapeutic benefit. Significant experimental work has already suggested that elimination of Human Leukocytes Antigen (HLA) expression and overexpression of immunomodulatory genes can impact survival of a variety of pluripotent stem cell-derived somatic cell types. Limited work published to date focuses on stem cell-derived islets and work in a number of labs is ongoing. Rapid progress is occurring in the genome editing of human pluripotent stem cells and their progeny focused on evading destruction by the immune system in transplantation models, and while much research is still needed, there is no doubt the combined technologies of genome editing and stem cell therapy will profoundly impact transplantation medicine in the future.

CRISPR screening uncovers a central requirement for HHEX in pancreatic lineage commitment and plasticity restriction.

The pancreas and liver arise from a common pool of progenitors. However, the underlying mechanisms that drive their lineage diversification from the foregut endoderm are not fully understood. To tackle this question, we undertook a multifactorial approach that integrated human pluripotent-stem-cell-guided differentiation, genome-scale CRISPR-Cas9 screening, single-cell analysis, genomics and proteomics. We discovered that HHEX, a transcription factor (TF) widely recognized as a key regulator of liver development, acts as a gatekeeper of pancreatic lineage specification. HHEX deletion impaired pancreatic commitment and unleashed an unexpected degree of cellular plasticity towards the liver and duodenum fates. Mechanistically, HHEX cooperates with the pioneer TFs FOXA1, FOXA2 and GATA4, shared by both pancreas and liver differentiation programmes, to promote pancreas commitment, and this cooperation restrains the shared TFs from activating alternative lineages. These findings provide a generalizable model for how gatekeeper TFs like HHEX orchestrate lineage commitment and plasticity restriction in broad developmental contexts.

Efficient Detection of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) from Exhaled Breath.

Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) is transmitted through airborne particles in exhaled breath, causing severe respiratory disease, coronavirus disease-2019 (COVID-19), in some patients. Samples for SARS-CoV-2 testing are typically collected by nasopharyngeal swab, with the virus detected by PCR; however, patients can test positive for 3 months after infection. Without the capacity to assay SARS-CoV-2 in breath, it is not possible to understand the risk for transmission from infected individuals. To detect virus in breath, the Bubbler-a breathalyzer that reverse-transcribes RNA from SARS-CoV-2 particles into a sample-specific barcoded cDNA-was developed. In a study of 70 hospitalized patients, the Bubbler was both more predictive of lower respiratory tract involvement (abnormal chest X-ray) and less invasive than alternatives. Samples tested using the Bubbler were threefold more enriched for SARS-CoV-2 RNA than were samples from tongue swabs, implying that virus particles were being directly sampled. The barcode-enabled Bubbler was used for simultaneous diagnosis in large batches of pooled samples at a lower limit of detection of 334 genomic copies per sample. Diagnosis by sequencing can provide additional information, such as viral load and strain identity. The Bubbler was configured to sample nucleic acids in water droplets circulating in air, demonstrating its potential in environmental monitoring and the protective effect of adequate ventilation.

Evaluating Closures of Fresh Fruit and Vegetable Vendors During the COVID-19 Pandemic: Methodology and Preliminary Results Using Omnidirectional Street View Imagery.

BACKGROUND: The COVID-19 pandemic has significantly disrupted the food retail environment. However, its impact on fresh fruit and vegetable vendors remains unclear; these are often smaller, more community centered, and may lack the financial infrastructure to withstand supply and demand changes induced by such crises. OBJECTIVE: This study documents the methodology used to assess fresh fruit and vegetable vendor closures in New York City (NYC) following the start of the COVID-19 pandemic by using Google Street View, the new Apple Look Around database, and in-person checks. METHODS: In total, 6 NYC neighborhoods (in Manhattan and Brooklyn) were selected for analysis; these included two socioeconomically advantaged neighborhoods (Upper East Side, Park Slope), two socioeconomically disadvantaged neighborhoods (East Harlem, Brownsville), and two Chinese ethnic neighborhoods (Chinatown, Sunset Park). For each neighborhood, Google Street View was used to virtually walk down each street and identify vendors (stores, storefronts, street vendors, or wholesalers) that were open and active in 2019 (ie, both produce and vendor personnel were present at a location). Past vendor surveillance (when available) was used to guide these virtual walks. Each identified vendor was geotagged as a Google Maps pinpoint that research assistants then physically visited. Using the "notes" feature of Google Maps as a data collection tool, notes were made on which of three categories best described each vendor: (1) open, (2) open with a more limited setup (eg, certain sections of the vendor unit that were open and active in 2019 were missing or closed during in-person checks), or (3) closed/absent. RESULTS: Of the 135 open vendors identified in 2019 imagery data, 35% (n=47) were absent/closed and 10% (n=13) were open with more limited setups following the beginning of the COVID-19 pandemic. When comparing boroughs, 35% (28/80) of vendors in Manhattan were absent/closed, as were 35% (19/55) of vendors in Brooklyn. Although Google Street View was able to provide 2019 street view imagery data for most neighborhoods, Apple Look Around was required for 2019 imagery data for some areas of Park Slope. Past surveillance data helped to identify 3 additional established vendors in Chinatown that had been missed in street view imagery. The Google Maps "notes" feature was used by multiple research assistants simultaneously to rapidly collect observational data on mobile devices. CONCLUSIONS: The methodology employed enabled the identification of closures in the fresh fruit and vegetable retail environment and can be used to assess closures in other contexts. The use of past baseline surveillance data to aid vendor identification was valuable for identifying vendors that may have been absent or visually obstructed in the street view imagery data. Data collection using Google Maps likewise has the potential to enhance the efficiency of fieldwork in future studies.

A More Efficient Method for Synthetic Textile Fiber Analysis Using Polarized Light Microscopy.

The efficiency of conventional polarized light microscopy (PLM) methods for analyzing synthetic fiber evidence analyses is improved. Historically, using PLM for fiber identification relied on measuring refractive index. This prior PLM technology is reliable, but it is not efficient. Most fibers are optically anisotropic, having two principal refractive index values, N(High) and N(Low) . When the fiber is mounted in intermediate refractive index medium, efficiency is improved by observing the change in contrast while the polarized light's vector is rotated relative to the fiber's axis. Minimum contrast occurs when the refractive indices of the mounting medium and fiber are equal. This angle of equality is determined by orienting the fiber's highest refractive index parallel to the polarized light's electric field vector, rotating the fiber or polarizing element, observing minimum contrast and measuring the angle of equality. This method is rapid, reduces remounting fibers in different mounting media and provides a quantitative measure for fiber comparisons.

Fecal calprotectin concentrations in cancer patients with Clostridium difficile infection.

Fecal calprotectin (fCPT) has been used as a surrogate marker for assessment of intestinal inflammation. We explore the utility of fCPT values as a diagnostic aid in cancer patients with suspected Clostridium difficile infection (CDI). A total of 232 stool specimens submitted for GeneXpert C. difficile PCR testing were included in the study. All specimens were tested for fCPT and toxin/GDH antigens. Clinical severity of CDI cases was determined by the IDSA/SHEA criteria. Significant differences of median fCPT values between CDI (n = 117, Median 183.6 µg/g) and non-CDI (n = 115, 145.6 µg/g, p = 0.006) patients were seen. In CDI patents, significantly lower fCPT values were found in patients with mild to moderate (n = 95, 182.1 µg/g) than those with severe and severe to complicated (n = 22, 218.5 µg/g, p = 0.014) scores, and among those that were toxin positive (n = 24, 200.2 µg/g) vs. toxin negative (n = 86, 182.8 µg/g, p = 0.044). Despite this overall trend, wide variations in fCPT values were found in all categories examined. A logistic regression analysis revealed that the fCPT values correlated independently with the severity of clinical manifestations (OR = 2.021, 95%CI = 1.132-3.608); however, it did not correlate with other clinical outcomes. Our study findings show that high fecal calprotectin levels correlate with toxin-positive and clinically severe CDI; however, wide variations in individual measurements preclude establishment of reliable cut-offs for routine diagnostic use in cancer patients.

Identification and Characterization of Clostridium difficile Sequence Type 37 Genotype by Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry.

Clostridium difficile multilocus sequence type 37 (ST37), which mainly corresponds to ribotype 017, has been a dominant genotype circulating in China. In this study, we report the use of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) to analyze and characterize 204 C. difficile clinical isolates, including 49 ST37 and 155 non-ST37 isolates collected in China and other countries. The distributions of two major protein peaks (m/z 3,242 and 3,286) were significantly different between ST37 and non-ST37 prototype strains and clinical isolates. This difference was reproducible when analysis was performed on different colonies in different runs. This finding was repeated and confirmed by both bioMérieux Vitek MS and Bruker Microflex LT systems on isolates recovered from a variety of geographic regions worldwide. The combination of the two peaks was present in 47 of 49 ST37 isolates, resulting in a sensitivity of 95.9%. In contrast, the peak combination was absent in 153 of 155 non-ST37 isolates, resulting in a specificity of 98.7%. Our results suggest that MALDI-TOF MS is a rapid and reliable tool to identify C. difficile genotype ST37. Work is in progress to characterize the two molecules having peaks at m/z 3,242 and 3,286, which appear to be specific to C. difficile genotype ST37.

Epigenetic Reprogramming Strategies to Reverse Global Loss of 5-Hydroxymethylcytosine, a Prognostic Factor for Poor Survival in High-grade Serous Ovarian Cancer.

Purpose: A major challenge in platinum-based cancer therapy is the clinical management of chemoresistant tumors, which have a largely unknown pathogenesis at the level of epigenetic regulation.Experimental Design: We evaluated the potential of using global loss of 5-hydroxymethylcytosine (5-hmC) levels as a novel diagnostic and prognostic epigenetic marker to better assess platinum-based chemotherapy response and clinical outcome in high-grade serous tumors (HGSOC), the most common and deadliest subtype of ovarian cancer. Furthermore, we identified a targetable pathway to reverse these epigenetic changes, both genetically and pharmacologically.Results: This study shows that decreased 5-hmC levels are an epigenetic hallmark for malignancy and tumor progression in HGSOC. In addition, global 5-hmC loss is associated with a decreased response to platinum-based chemotherapy, shorter time to relapse, and poor overall survival in patients newly diagnosed with HGSOC. Interestingly, the rescue of 5-hmC loss restores sensitivity to platinum chemotherapy in vitro and in vivo, decreases the percentage of tumor cells with cancer stem cell markers, and increases overall survival in an aggressive animal model of platinum-resistant disease.Conclusions: Consequently, a global analysis of patient 5-hmC levels should be included in future clinical trials, which use pretreatment with epigenetic adjuvants to elevate 5-hmC levels and improve the efficacy of current chemotherapies. Identifying prognostic epigenetic markers and altering chemotherapeutic regimens to incorporate DNMTi pretreatment in tumors with low 5-hmC levels could have important clinical implications for newly diagnosed HGSOC disease. Clin Cancer Res; 24(6); 1389-401. ©2017 AACR.

Parallel Validation of Three Molecular Devices for Simultaneous Detection and Identification of Influenza A and B and Respiratory Syncytial Viruses.

Rapid identification of respiratory pathogens, such as influenza virus A (FluA), influenza virus B (FluB), and respiratory syncytial virus (RSV), reduces unnecessary antimicrobial use and enhances infection control practice. We performed a comparative evaluation of three molecular methods: (i) the Aries Flu A/B & RSV, (ii) the Xpert Xpress Flu/RSV, and (iii) the Cobas Flu A/B & RSV assays. The clinical performances of the three methods were evaluated using 200 remnant nasopharyngeal swab (NPS) specimens against a combined reference standard. The limits of detection (LODs) were determined using FluA, FluB, and RSV control strains with known titers. The 95% LODs were between 1.702 and 0.0003 50% tissue culture infective dose (TCID50), with no significant differences revealed among the three assays. Perfect qualitative detection agreement was obtained in the reproducibility study. The Cobas assay failed at the first run on 13 clinical specimens, resulting in an invalid rate of 6.5%. The sensitivities and specificities for all assays were 96.0 to 100.0% and 99.3 to 100% for all three viruses. For on-demand single-specimen and batched 12-specimen workflows, the test turnaround times were 115.5 and 128.8 min for the Aries assay (12 sample capacity), 34.2 and 44.2 min for the Xpress assay (16 sample capacity), and 21.0 and 254.4 min for the Cobas assay (one instrument), respectively. In summary, the Aries, Xpress, and Cobas Liat assays demonstrated excellent sensitivities and specificities for simultaneous detection and identification of FluA, FluB, and RSV from NPS specimens in cancer patients. Test turnaround time was significantly shorter on the Xpress when instrument scalability is unlimited.

Rapid Molecular Detection and Differentiation of Influenza Viruses A and B.

Influenza is a contagious respiratory illness caused by influenza viruses A and B in humans and causes a significant amount of morbidity and mortality every year. The Influenza A and B assay was the first CLIA-waived molecular rapid flu test available. The Influenza A and B test works by employing isothermal amplification with influenza-specific primers followed by target detection with molecular beacon probes. Here, the performance of the Influenza A and B assay on frozen, archived nasopharyngeal swab (NPS) specimens stored in viral transport medium (VTM) were compared to a respiratory panel assay. The performance of the Influenza A and B assay was evaluated by comparing the results to the respiratory panel reference method. The sensitivity for total influenza virus A was 67.5% (95% CI (CI), 56.6-78.5) and the specificity was 86.9% (CI, 71.0-100). For influenza virus B testing, the sensitivity and specificity were 90.2% (CI, 68.5-100) and 98.8% (CI, 68.5-100), respectively. This system has the advantage of a significantly shorter test time than any other currently available molecular assay and the simple, pipette-free procedure runs on a fully integrated, closed, small-footprint system. Overall, the Influenza A and B assay evaluated in this study has the potential to serve as a point-of-care rapid influenza diagnostic test.

Detection of HPV related oropharyngeal cancer in oral rinse specimens.

BACKGROUND: The majority of patients diagnosed with oropharyngeal squamous cell cancer (OPSCC) are due to HPV infection. At present, there are no reliable tests for screening HPV in patients with OPSCC. The objective of this study was to assess the Cobas® HPV Test on oral rinse specimens as an early, non-invasive tool for HPV-related OPSCC. METHODS: Oral rinse specimens were collected from 187 patients (45 with OPSCC, 61 with oral cavity SCC (OCSCC) and 81 control patients who had benign or malignant thyroid nodules) treated at MSKCC. The Cobas® HPV Test was used to detect 14 high-risk HPV types in these samples. Performance of the HPV Test was correlated with p16 tumor immunohistochemistry as gold standard. RESULTS: 91.1% of the oropharynx cancer patients had p16 positive tumors compared to 3.3% of oral cavity cancer. Of the 81 control patients, 79 (97.5%) had no HPV in their oral rinse giving a specificity of the HPV test of 98%. For the combined oral cavity oropharynx cancer cohort, the sensitivity, specificity, positive predictive value and negative predictive value of the HPV Test were 79.1%, 90.5%, 85.0% and 86.4% respectively when p16 immunohistochemistry was used as the reference. CONCLUSION: The Cobas® HPV Test on oral rinse is a highly specific and potentially sensitive test for oropharyngeal cancer and may be a potentially useful screening test for early oropharyngeal cancer. IMPACT: We describe an oral rinse test for the detection of HPV related oropharyngeal cancer.

Laboratory Diagnosis of Central Nervous System Infection.

Central nervous system (CNS) infections are potentially life threatening if not diagnosed and treated early. The initial clinical presentations of many CNS infections are non-specific, making a definitive etiologic diagnosis challenging. Nucleic acid in vitro amplification-based molecular methods are increasingly being applied for routine microbial detection. These methods are a vast improvement over conventional techniques with the advantage of rapid turnaround and higher sensitivity and specificity. Additionally, molecular methods performed on cerebrospinal fluid samples are considered the new gold standard for diagnosis of CNS infection caused by pathogens, which are otherwise difficult to detect. Commercial diagnostic platforms offer various monoplex and multiplex PCR assays for convenient testing of targets that cause similar clinical illness. Pan-omic molecular platforms possess potential for use in this area. Although molecular methods are predicted to be widely used in diagnosing and monitoring CNS infections, results generated by these methods need to be carefully interpreted in combination with clinical findings. This review summarizes the currently available armamentarium of molecular assays for diagnosis of central nervous system infections, their application, and future approaches.

Transcriptome response to nitrosative stress in Rhodobacter sphaeroides 2.4.1.

The facultative photosynthetic bacterium Rhodobacter sphaeroides 2.4.1 has a nitric oxide-response transcriptional regulator, NnrR, and nitric oxide reductase (NOR), although it is incapable of denitrification. To investigate at the genomic level the physiological response to nitrosative stress of R. sphaeroides, the transcriptome profiles of strain 2.4.1 and its NnrR mutant were analyzed before and after exposure to nitrosating agents, S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP), under microaerobic conditions. GSNO and SNP affected the expression of different but overlapping sets of genes. Only a limited number of these genes, including the genes for NOR, were under the control of NnrR, and those genes were significantly upregulated by GSNO and by SNP. The oxygen-responsive regulator FnrL and a predicted iron-sensing regulator were perhaps also involved in the transcriptome response to reactive nitrogen species. Some genes, including hemN for heme biosynthesis, were subject to dual regulation by NnrR and FnrL.

Revealing linear aggregates of light harvesting antenna proteins in photosynthetic membranes.

How light energy is harvested in a natural photosynthetic membrane through energy transfer is closely related to the stoichiometry and arrangement of light harvesting antenna proteins in the membrane. The specific photosynthetic architecture facilitates a rapid and efficient energy transfer among the light harvesting proteins (LH2 and LH1) and to the reaction center. Here we report the identification of linear aggregates of light harvesting proteins, LH2, in the photosynthetic membranes under ambient conditions by using atomic force microscopy (AFM) imaging and spectroscopic analysis. Our results suggest that the light harvesting protein, LH2, can exist as linear aggregates of 4 +/- 2 proteins in the photosynthetic membranes and that the protein distributions are highly heterogeneous. In the photosynthetic membranes examined in our measurements, the ratio of the aggregated to the nonaggregated LH2 proteins is about 3:1 to 5:1 depending on the intensity of the illumination used during sample incubation and on the bacterial species. AFM images further identify that the LH2 proteins in the linear aggregates are monotonically tilted at an angle 4 +/- 2 degrees from the plane of the photosynthetic membranes. The aggregates result in red-shifted absorption and emission spectra that are measured using various mutant membranes, including an LH2 knockout, LH1 knockout, and LH2 at different population densities. Measuring the fluorescence lifetimes of purified LH2 and LH2 in membranes, we have observed that the LH2 proteins in membranes exhibit biexponential lifetime decays whereas the purified LH2 proteins gave single exponential lifetime decays. We attribute that the two lifetime components originate from the existence of both aggregated and nonaggregated LH2 proteins in the photosynthetic membranes.

Half-Site DNA sequence and spacing length contributions to PrrA binding to PrrA site 2 of RSP3361 in Rhodobacter sphaeroides 2.4.1.

The consensus DNA binding sequence for PrrA, a global regulator in Rhodobacter sphaeroides 2.4.1, is poorly defined. We have performed mutational analysis of PrrA site 2, of the RSP3361 gene, to which PrrA binds in vitro (J. M. Eraso and S. Kaplan, J. Bacteriol. 191:4341-4352, 2009), to further define the consensus sequence for DNA binding. Two half-sites of equal length, containing 6 nucleotides each, were required for PrrA binding to this DNA sequence. Systematic nucleotide substitutions in both inverted half-sites led to a decrease in binding affinity of phosphorylated PrrA in vitro, the level of which was dependent on the substitution. The reduced binding affinities were confirmed by competition experiments and led to proportional decreases in the expression of lacZ transcriptional fusions to the RSP3361 gene in vivo. The 5-nucleotide spacer region between the half-sites was found to be optimal for PrrA binding to the wild-type half-sites, as shown by decreased PrrA DNA binding affinities to synthetic DNA sequences without spacer regions or with spacer regions ranging from 1 to 10 nucleotides. The synthetic spacer region alleles also showed decreased gene expression in vivo when analyzed using lacZ transcriptional fusions. We have studied three additional DNA sequences to which PrrA binds in vitro. They are located in the regulatory regions of genes positively regulated by PrrA and contain spacer regions with 5 or 8 nucleotides. We demonstrate that PrrA can bind in vitro to DNA sequences with different lengths in the spacer regions between the half-sites.

Regulation of gene expression by PrrA in Rhodobacter sphaeroides 2.4.1: role of polyamines and DNA topology.

In the present study, we show in vitro binding of PrrA, a global regulator in Rhodobacter sphaeroides 2.4.1, to the PrrA site 2, within the RSP3361 locus. Specific binding, as shown by competition experiments, requires the phosphorylation of PrrA. The binding affinity of PrrA for site 2 was found to increase 4- to 10-fold when spermidine was added to the binding reaction. The presence of extracellular concentrations of spermidine in growing cultures of R. sphaeroides gave rise to a twofold increase in the expression of the photosynthesis genes pucB and pufB, as well as the RSP3361 gene, under aerobic growth conditions, as shown by the use of lacZ transcriptional fusions, and led to the production of light-harvesting spectral complexes. In addition, we show that negative supercoiling positively regulates the expression of the RSP3361 gene, as well as pucB. We show the importance of supercoiling through an evaluation of the regulation of gene expression in situ by supercoiling, in the case of the former gene, as well as using the DNA gyrase inhibitor novobiocin. We propose that polyamines and DNA supercoiling act synergistically to regulate expression of the RSP3361 gene, partly by affecting the affinity of PrrA binding to the PrrA site 2 within the RSP3361 gene.