Template DNA Strand Research Articles

Fractional‐nucleotide translocation in sequence‐dependent pausing by RNA polymerase: Single‐molecule picometer‐resolution nanopore tweezers (SPRNT)

Single‐molecule picometer‐resolution nanopore tweezers (SPRNT) enables monitoring of translocation of a nucleic‐acid motor protein on a nucleic‐acid track with sequence registration, sub‐nucleotide spatial resolution, sub‐millisecond temporal resolution, and the ability to apply assisting and opposing forces.We have demonstrated the ability of SPRNT to monitor translocation of RNA polymerase (RNAP) relative to the DNA template strand, the DNA non‐template strand, and the RNA product strand in transcription, and we have applied SPRNT to analyze RNAP translocation in transcription elongation and sequence‐dependent transcriptional pausing.The results show that sequence‐dependent transcriptional pausing involves a “half‐translocated” state in which RNAP translocates relative to the DNA template strand by 0.5 nucleotides. The “half‐translocated” state is unable to bind the next NTP substrate, presumably because RNAP translocation by 0.5 nt does not align the next template‐strand nucleotide with the RNAP active‐center NTP addition site. The half‐translocated state interconverts rapidly (~0.1–1 s) with the “pre‐translocated” state and converts slowly (~1 s) to the NTP‐binding‐competent “post‐translocated state.” In the presence of saturating NTPs, conversion to the post‐translocated state is followed by pause escape. In the presence of limiting NTPs, conversion to the post‐translocated state is followed by return to interconverting half‐translocated and pre‐translocated states and continued pausing.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Label-free and dye-free detection of target DNA based on intrinsic fluorescence of the (3+1) interlocked bimolecular G-quadruplexes

The intrinsic fluorescence of the interlocked bimolecular DNA G-quadruplex (93del4T) was utilized to achieve label-free and non-toxic detection of target DNA. The designed probe consists of a single stranded DNA template that hybridizes with the sequence of 93del4T at 5′ end forming partial complementary duplex and leaving single strand overhang at 3′ terminus to recognize target DNA molecule. Once the target DNA hybridizes with the probe to form another part of duplex at 3′ terminus, exonuclease Ⅲ will catalyze the stepwise removal of nucleotides from the blunt 3′ terminus, consecutively liberating the target DNA and the sequence of 93del4T. The released target DNAs can recycle to bind more probes and release more 93del4T that can fold into G-quadruplexes to amplify fluorescence signals. As a result, quantitative detection of the target DNA in human serum has been achieved according to fluorescent signal intensities. In comparison to other methods, this strategy is simple, rapid, inexpensive and toxic free.

Structures of an RNA polymerase promoter melting intermediate elucidate DNA unwinding.

A key regulated step of transcription is promoter melting by RNA polymerase (RNAP) to form the open promoter complex1-3. To generate the open complex, the conserved catalytic core of the RNAP combines with initiation factors to locate promoter DNA, unwind 12-14 base pairs of the DNA duplex and load the template-strand DNA into the RNAP active site. Formation of the open complex is a multi-step process during which transient intermediates of unknown structure are formed4-6. Here we present cryo-electron microscopy structures of bacterial RNAP-promoter DNA complexes, including structures of partially melted intermediates. The structures show that late steps of promoter melting occur within the RNAP cleft, delineate key roles for fork-loop 2and switch 2-universal structural features of RNAP-in restricting access of DNA to the RNAP active site, and explain why clamp opening is required to allow entry of single-stranded template DNA into the active site. The key roles of fork-loop 2 and switch 2 suggest a common mechanism for late steps in promoter DNA opening to enable gene expression across all domains of life.

RNA polymerase III subunits C37/53 modulate rU:dA hybrid 3' end dynamics during transcription termination.

RNA polymerase (RNAP) III synthesizes tRNAs and other transcripts, and mutations to its subunits cause human disorders. The RNAP III subunit-heterodimer C37/53 functions in initiation, elongation and in termination-associated reinitiation with subunit C11. C37/53 is related to heterodimers associated with RNAPs I and II, and C11 is related to TFIIS and Rpa12.2, the active site RNA 3′ cleavage factors for RNAPs II and I. Critical to termination is stability of the RNA:DNA hybrid bound in the active center, which is loose for RNAP III relative to other RNAPs. Here, we examined RNAP III lacking C37/53/C11 and various reconstituted forms during termination. First, we established a minimal terminator as 5T and 3A on the non-template and template DNA strands, respectively. We demonstrate that C11 stimulates termination, and does so independently of its RNA cleavage activity. We found that C37/53 sensitizes RNAP III termination to RNA:DNA hybrid strength and promotes RNA 3′ end pairing/annealing with the template. The latter counteracts C11-insensitive arrest in the proximal part of the oligo(T)-tract, promoting oligo(rU:dA) extension toward greater hybrid instability and RNA release. The data also indicate that RNA 3′ end engagement with the active site is a determinant of termination. Broader implications are also discussed.

DNA Templated Metal Nanoclusters: From Emergent Properties to Unique Applications.

Metal nanoclusters containing a few to several hundred atoms with sizes ranging from sub-nanometer to ∼2 nm occupy an intermediate size regime that bridges larger plasmonic nanoparticles and smaller metal complexes. With strong quantum confinement, metal nanoclusters exhibit molecule-like properties. This Account focuses on noble metal nanoclusters that are synthesized within a single stranded DNA template. Compared to other ligand protected metal nanoclusters, DNA-templated metal nanoclusters manifest intriguing physical and chemical properties that are heavily influenced by the design of DNA templates. For example, DNA-templated silver nanoclusters can show bright fluorescence, tunable emission colors, and enhanced stability by tuning the sequence of the encapsulating DNA template. DNA-templated gold nanoclusters can also serve as excellent cocatalysts, which are integratable with other biocatalysts such as enzymes. In this Account, DNA-templated silver and gold nanoclusters are selected as paradigm systems to showcase their emergent properties and unique applications. We first discuss the DNA-templated silver nanoclusters with a focus on the creation of a complementary palette of emission colors, which has potential applications for multiplex assays. The importance of the DNA template toward enhanced stability of silver nanoclusters is also demonstrated. We then introduce a special class of activable fluorescence probes that are based on the fluorescence turn-on phenomena of DNA-templated silver nanoclusters, which are named nanocluster beacons (NCBs). NCBs have distinct advantages over molecular beacons for nucleic acid detection, and their emission mechanisms are also discussed in detail. We then discuss a universal method of creating novel DNA-silver nanocluster aptamers for protein detection with high specificity. The remainder of the Account is devoted to the DNA-templated gold nanoclusters. We demonstrate that DNA-gold nanoclusters can serve as enhancers for enzymatic reduction of oxygen, which is one of the most important reactions in biofuel cells. Although DNA-templated metal nanoclusters are still in their infancy, we anticipate they will emerge as a new type of functional nanomaterial with wide applications in biology and energy science. Future research will focus on the synthesis of size selected DNA-metal nanoclusters with atomic monodispersity, structural determination of different sized DNA-metal nanoclusters, and establishment of structure-property correlations. Some long-standing mysteries, such as the origin of fluorescence and mechanism for emission color tunability, constitute the central questions regarding the photophysical properties of DNA-metal nanoclusters. On the application side, more studies are required to understand the interaction between nanocluster and biological systems. In the foreseeable future, one can expect that new biosensors, catalysts, and functional devices will be invented based on the intriguing properties of well-designed DNA-metal nanoclusters and their composites. Overall, DNA-metal nanoclusters can add additional spotlights into the highly vibrant field of ligand protected, quantum sized metal nanoclusters.

Region 3.2 of the σ factor controls the stability of rRNA promoter complexes and potentiates their repression by DksA.

The σ factor drives promoter recognition by bacterial RNA polymerase (RNAP) and is also essential for later steps of transcription initiation, including RNA priming and promoter escape. Conserved region 3.2 of the primary σ factor (‘σ finger’) directly contacts the template DNA strand in the open promoter complex and facilitates initiating NTP binding in the active center of RNAP. Ribosomal RNA promoters are responsible for most RNA synthesis during exponential growth but should be silenced during the stationary phase to save cell resources. In Escherichia coli, the silencing mainly results from the action of the secondary channel factor DksA, which together with ppGpp binds RNAP and dramatically decreases the stability of intrinsically unstable rRNA promoter complexes. We demonstrate that this switch depends on the σ finger that destabilizes RNAP–promoter interactions. Mutations in the σ finger moderately decrease initiating NTP binding but significantly increase promoter complex stability and reduce DksA affinity to the RNAP–rRNA promoter complex, thus making rRNA transcription less sensitive to DksA/ppGpp both in vitro and in vivo. Thus, destabilization of rRNA promoter complexes by the σ finger makes them a target for robust regulation by the stringent response factors under stress conditions.

R-Loops in Motor Neuron Diseases.

R loops are transient three-stranded nucleic acid structures that form physiologically during transcription when a nascent RNA transcript hybridizes with the DNA template strand, leaving a single strand of displaced nontemplate DNA. However, aberrant persistence of R-loops can cause DNA damage by inducing genomic instability. Indeed, evidence has emerged that R-loops might represent a key element in the pathogenesis of human diseases, including cancer, neurodegeneration, and motor neuron disorders. Mutations in genes directly involved in R-loop biology, such as SETX (senataxin), or unstable DNA expansion eliciting R-loop generation, such as C9ORF72 HRE, can cause DNA damage and ultimately result in motor neuron cell death. In this review, we discuss current advancements in this field with a specific focus on motor neuron diseases associated with deregulation of R-loop structures. These mechanisms can represent novel therapeutic targets for these devastating, incurable diseases.

Isothermal amplification using modified primers for rapid electrochemical analysis of coeliac disease associated DQB1*02 HLA allele

DNA biosensors are attractive tools for genetic analysis as there is an increasing need for rapid and low-cost DNA analysis, primarily driven by applications in personalized pharmacogenomics, clinical diagnostics, rapid pathogen detection, food traceability and forensics. A rapid electrochemical genosensor detection methodology exploiting a combination of modified primers for solution-phase isothermal amplification, followed by rapid detection via hybridization on gold electrodes is reported. Modified reverse primers, exploiting a C18 spacer between the primer-binding site and an engineered single stranded tail, are used in a recombinase polymerase amplification reaction to produce an amplicon with a central duplex flanked by two single stranded tails. These tails are designed to be complementary to a gold electrode tethered capture oligo probe as well as a horseradish peroxidase labelled reporter oligo probe. The time required for hybridization of the isothermally generated amplicons with each of the immobilized and reporter probes was optimised to be 2 min, in both cases. The effect of amplification time and the limit of detection were evaluated using these hybridization times for both single stranded and double stranded DNA templates. The best detection limit of 70 fM for a ssDNA template was achieved using 45 min amplification, whilst for a dsDNA template, just 30 min amplification resulted in a slightly lower detection limit of 14 fM, whilst both 20 and 45 min amplification times were observed to provide detection limits of 71 and 72 fM, respectively, but 30 and 45 min amplification resulted in a much higher signal and sensitivity. The genosensor was applied to genomic DNA and real patient and control blood samples for detection of the coeliac disease associated DQB1*02 HLA allele, as a model system, demonstrating the possibility to carry out molecular diagnostics, combining amplification and detection in a rapid and facile manner.

Enzymatic Synthesis of Self-assembled Dicer Substrate RNA Nanostructures for Programmable Gene Silencing

Enzymatic synthesis of RNA nanostructures is achieved by isothermal rolling circle transcription (RCT). Each arm of RNA nanostructures provides a functional role of Dicer substrate RNA inducing sequence specific RNA interference (RNAi). Three different RNAi sequences (GFP, RFP, and BFP) are incorporated within the three-arm junction RNA nanostructures (Y-RNA). The template and helper DNA strands are designed for the large-scale in vitro synthesis of RNA strands to prepare self-assembled Y-RNA. Interestingly, Dicer processing of Y-RNA is highly influenced by its physical structure and different gene silencing activity is achieved depending on its arm length and overhang. In addition, enzymatic synthesis allows the preparation of various Y-RNA structures using a single DNA template offering on demand regulation of multiple target genes.

Kinetic Mechanism of DNA Polymerases: Contributions of Conformational Dynamics and a Third Divalent Metal Ion.

Faithful transmission and maintenance of genetic material is primarily fulfilled by DNA polymerases. During DNA replication, these enzymes catalyze incorporation of deoxynucleotides into a DNA primer strand based on Watson-Crick complementarity to the DNA template strand. Through the years, research on DNA polymerases from every family and reverse transcriptases has revealed structural and functional similarities, including a conserved domain architecture and purported two-metal-ion mechanism for nucleotidyltransfer. However, it is equally clear that DNA polymerases possess distinct differences that often prescribe a particular cellular role. Indeed, a unified kinetic mechanism to explain all aspects of DNA polymerase catalysis, including DNA binding, nucleotide binding and incorporation, and metal-ion-assisted nucleotidyltransfer (i.e., chemistry), has been difficult to define. In particular, the contributions of enzyme conformational dynamics to several mechanistic steps and their implications for replication fidelity are complex. Moreover, recent time-resolved X-ray crystallographic studies of DNA polymerases have uncovered a third divalent metal ion present during DNA synthesis, the function of which is currently unclear and debated within the field. In this review, we survey past and current literature describing the structures and kinetic mechanisms of DNA polymerases from each family to explore every major mechanistic step while emphasizing the impact of enzyme conformational dynamics on DNA synthesis and replication fidelity. This also includes brief insight into the structural and kinetic techniques utilized to study DNA polymerases and RTs. Furthermore, we present the evidence for the two-metal-ion mechanism for DNA polymerase catalysis prior to interpreting the recent structural findings describing a third divalent metal ion. We conclude by discussing the diversity of DNA polymerase mechanisms and suggest future characterization of the third divalent metal ion to dissect its role in DNA polymerase catalysis.

Variable termination sites of DNA polymerases encountering a DNA-protein cross-link.

DNA-protein cross-links (DPCs) are important DNA lesions induced by endogenous crosslinking agents such as formaldehyde or acetaldehyde, as well as ionizing radiation, cancer chemotherapeutic drugs, and abortive action of some enzymes. Due to their very bulky nature, they are expected to interfere with DNA and RNA synthesis and DNA repair. DPCs are highly genotoxic and the ability of cells to deal with them is relevant for many chemotherapeutic interventions. However, interactions of DNA polymerases with DPCs have been poorly studied due to the lack of a convenient experimental model. We have used NaBH4-induced trapping of E. coli formamidopyrimidine-DNA glycosylase with DNA to construct model DNA polymerase substrates containing a DPC in single-stranded template, or in the template strand of double-stranded DNA, or in the non-template (displaced) strand of double-stranded DNA. Nine DNA polymerases belonging to families A, B, X, and Y were studied with respect to their behavior upon encountering a DPC: Klenow fragment of E. coli DNA polymerase I, Thermus aquaticus DNA polymerase I, Pyrococcus furiosus DNA polymerase, Sulfolobus solfataricus DNA polymerase IV, human DNA polymerases β, κ and λ, and DNA polymerases from bacteriophages T4 and RB69. Although none were able to fully bypass DPCs in any context, Family B DNA polymerases (T4, RB69) and Family Y DNA polymerase IV were able to elongate the primer up to the site of the cross-link if a DPC was located in single-stranded template or in the displaced strand. In other cases, DNA synthesis stopped 4–5 nucleotides before the site of the cross-link in single-stranded template or in double-stranded DNA if the polymerases could displace the downstream strand. We suggest that termination of DNA polymerases on a DPC is mostly due to the unrelieved conformational strain experienced by the enzyme when pressing against the cross-linked protein molecule.

Detection of PCR-Amplified Tuberculosis DNA Fragments with Polyelectrolyte-Modified Field-Effect Sensors.

Field-effect-based electrolyte-insulator-semiconductor (EIS) sensors were modified with a bilayer of positively charged weak polyelectrolyte (poly(allylamine hydrochloride) (PAH)) and probe single-stranded DNA (ssDNA) and are used for the detection of complementary single-stranded target DNA (cDNA) in different test solutions. The sensing mechanism is based on the detection of the intrinsic molecular charge of target cDNA molecules after the hybridization event between cDNA and immobilized probe ssDNA. The test solutions contain synthetic cDNA oligonucleotides (with a sequence of tuberculosis mycobacteria genome) or PCR-amplified DNA (which origins from a template DNA strand that has been extracted from Mycobacterium avium paratuberculosis-spiked human sputum samples), respectively. Sensor responses up to 41 mV have been measured for the test solutions with DNA, while only small signals of ∼5 mV were detected for solutions without DNA. The lower detection limit of the EIS sensors was ∼0.3 nM, and the sensitivity was ∼7.2 mV/decade. Fluorescence experiments using SybrGreen I fluorescence dye support the electrochemical results.

Molecular Mechanism of Transcription Transcription‐Coupled Repair

Progression of RNA polymerase II (Pol II) elongation along the DNA template strand can be blocked by a number of obstructions, including covalent DNA lesions, non‐canonical DNA structures, intrinsic arrest sequences, and small molecules or proteins bound to the DNA. These arrested transcriptional complexes, if not resolved in a timely manner, can be harmful to the cell and increase the risk of genomic instability.Eukaryotic transcription‐coupled DNA repair is an important sub‐pathway of nucleotide excision repair that preferentially removes DNA lesions from the template strand that block Pol II translocation. This process is initiated by Pol II arrested by DNA lesion and the recruitment of Cockayne Syndrome B protein (CSB) to the lesion‐arrested Pol II. However, the function and molecular mechanism of transcription‐coupled repair initiation have remained elusive.Here we report our recent structural and functional studies of lesion‐arrested Pol II and Pol II‐CSB complex. These structures provide important structural insights of how DNA lesions are recognized during transcription and the key roles of CSB in both transcription‐coupled repair and transcription elongation. These studies greatly advance our understanding of the molecular mechanism of transcription‐coupled DNA lesion recognition and transcription‐coupled repair initiation.Support or Funding InformationNIGMSThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Exploration of Conformational Selection During Translesion Synthesis: In Silico Studies of DinB

E. coli DNA Polymerase IV, also named DinB after its encoding gene, is a Y‐family DNA polymerase used by cells during stress‐induced mutagenesis. DinB functions as an error‐prone polymerase implicated in translesion synthesis. Kinetics studies have shown that DinB is more efficient at bypassing damaged DNA versus undamaged DNA, and that the polymerase is more effective at bypassing minor groove mutations, such as the N2‐furfuryl‐dG, than major groove mutations, such as the O6‐methylated‐dG. Recent hydrogen experiments suggest that DinB undergoes a conformational change only in the presence of select damages on the DNA template strand. These differentiations imply a possible mechanism of bypass discrimination, though discrete characteristic movements have not been identified. In this study, molecular dynamics (MD) simulations were used to explore these conformational movements through the generation and study of various systems of DNA/protein/incoming nucleotide combinations. A total of four systems were made: binary (DNA and protein), ternary‐CG (DNA, protein, correct incoming nucleotide), ternary O6‐methylated‐dG (deoxyguanosine with O6‐methylation on the template strand, protein, and correct incoming nucleotide), and binary O6‐methylated‐dG (deoxyguanosine with O6‐methylation on the template strand and protein). A ternary‐GG (DNA, protein, incorrect incoming nucleotide) system has been built, but has not yet been run through simulations. An N2‐furfuryl‐dG molecule was also built; however, the molecule requires further parameterization prior to dynamics run. The binary systems showed the highest levels of fluctuation, implying that, in lack of substrate, DinB has no conformational selectivity and is thus in a floppy and unrestrained state. Initially, the ternary O6‐methylated‐dG system seemed more similar to the ternary‐CG system than the binary system (the opposite of what was predicted). However, closer analysis of the ternary O6‐methylated‐dG system showed that residues key to stabilization of the incoming nucleotide were missing from the active site, suggesting an inability to reach catalytic competence without these residues to promote the appropriate conformational selection. Previously, it was believed that DinB adopted either an open‐inactive conformation (in the presence of a mutation or lack of substrate) or closed‐active conformation (no mutation and presence of proper substrate) in accordance with the induced‐fit theory of catalysis. However, our data suggest a less rigid breathing movement and mechanism of conformational selection as opposed to induced fit. Accordingly, data interpretation has moved from analysis of gross domain movements to analysis of the presence of key catalytic residues in the active site.Support or Funding InformationThis work was supported in part by the Rose M. Badgeley Residuary Charitable Trust Award and the Colette Mahoney Award to BSB.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Three-dimensional structural dynamics of DNA origami Bennett linkages using individual-particle electron tomography

Scaffolded DNA origami has proven to be a powerful and efficient technique to fabricate functional nanomachines by programming the folding of a single-stranded DNA template strand into three-dimensional (3D) nanostructures, designed to be precisely motion-controlled. Although two-dimensional (2D) imaging of DNA nanomachines using transmission electron microscopy and atomic force microscopy suggested these nanomachines are dynamic in 3D, geometric analysis based on 2D imaging was insufficient to uncover the exact motion in 3D. Here we use the individual-particle electron tomography method and reconstruct 129 density maps from 129 individual DNA origami Bennett linkage mechanisms at ~ 6–14 nm resolution. The statistical analyses of these conformations lead to understanding the 3D structural dynamics of Bennett linkage mechanisms. Moreover, our effort provides experimental verification of a theoretical kinematics model of DNA origami, which can be used as feedback to improve the design and control of motion via optimized DNA sequences and routing.

BLM helicase suppresses recombination at G-quadruplex motifs in transcribed genes

Bloom syndrome is a cancer predisposition disorder caused by mutations in the BLM helicase gene. Cells from persons with Bloom syndrome exhibit striking genomic instability characterized by excessive sister chromatid exchange events (SCEs). We applied single-cell DNA template strand sequencing (Strand-seq) to map the genomic locations of SCEs. Our results show that in the absence of BLM, SCEs in human and murine cells do not occur randomly throughout the genome but are strikingly enriched at coding regions, specifically at sites of guanine quadruplex (G4) motifs in transcribed genes. We propose that BLM protects against genome instability by suppressing recombination at sites of G4 structures, particularly in transcribed regions of the genome.

<i>In-Silico</i> Side-Directed Mutagenesis of Oxidoreductase from <i>Anoxybacillus sp.</i> SK3-4

Precisely, mutagenesis can introduce mutations into the target gene by using mismatch primers which are partially complementary to the template strand of DNA using polymerase chain reaction (PCR). Oxidoreductase enzymes are generally proteins that involved in oxidation-reduction reactions in biological systems. For this study, primary sequence analyses of oxidoreductase protein from Anoxybacillus sp. SK3-4 was conducted with the aim of generating functional information and theoretically improve catalytic stability of the protein by in-silico mutagenesis. The primary sequence of a novel protein with 386 amino acid residues was analyzed using Expasy-tool for translation of the amino acid sequence into a nucleotide gene sequence. Important catalytic binding sites of the protein were predicted using 3DLigandSite program, Pheres2 and Protein Bioedit servers for generating functional information of the protein. Site-directed mutagenesis (SDM) was used against the novel protein (oxidoreductase), in which two site mutations were created based on rational design. Amino acids; leucine (L) and histidine (H), involved in substrate and metal binding sites in the protein were substituted for isoleucine (I) and arginine (R) i.e. L138I and H280R, to check for significant change in the functional stability of the protein, thereby increasing the efficiency of the enzyme to help speed up the rate of chemical reactions.

Genome-wide mapping of sister chromatid exchange events in single yeast cells using Strand-seq.

Homologous recombination involving sister chromatids is the most accurate, and thus most frequently used, form of recombination-mediated DNA repair. Despite its importance, sister chromatid recombination is not easily studied because it does not result in a change in DNA sequence, making recombination between sister chromatids difficult to detect. We have previously developed a novel DNA template strand sequencing technique, called Strand-seq, that can be used to map sister chromatid exchange (SCE) events genome-wide in single cells. An increase in the rate of SCE is an indicator of elevated recombination activity and of genome instability, which is a hallmark of cancer. In this study, we have adapted Strand-seq to detect SCE in the yeast Saccharomyces cerevisiae. We provide the first quantifiable evidence that most spontaneous SCE events in wild-type cells are not due to the repair of DNA double-strand breaks.

Immunoprecipitation of RNA:DNA Hybrids from Budding Yeast.

During transcription, the nascent transcript behind an elongating RNA polymerase (RNAP) can invade the DNA duplex and hybridize with the complementary DNA template strand, generating a three-stranded "R-loop" structure, composed of an RNA:DNA duplex and an unpaired non-template DNA strand. R-loops can be strongly associated with actively transcribed loci by all RNAPs including the mitochondrial RNA polymerase (mtRNAP). In this chapter, we describe two protocols for the detection of RNA:DNA hybrids in living budding yeast cells, one that uses conventional chromatin immunoprecipitation (ChIP-qPCR) and one that uses DNA:RNA immunoprecipitation (DRIP-qPCR). Both protocols make use of the S9.6 antibody, which is believed to recognize the intermediate A/B helical RNA:DNA duplex conformation, with no sequence specificity.

A Thermus phage protein inhibits host RNA polymerase by preventing template DNA strand loading during open promoter complex formation.

RNA polymerase (RNAP) is a major target of gene regulation. Thermus thermophilus bacteriophage P23–45 encodes two RNAP binding proteins, gp39 and gp76, which shut off host gene transcription while allowing orderly transcription of phage genes. We previously reported the structure of the T. thermophilus RNAP•σA holoenzyme complexed with gp39. Here, we solved the structure of the RNAP•σA holoenzyme bound with both gp39 and gp76, which revealed an unprecedented inhibition mechanism by gp76. The acidic protein gp76 binds within the RNAP cleft and occupies the path of the template DNA strand at positions –11 to –4, relative to the transcription start site at +1. Thus, gp76 obstructs the formation of an open promoter complex and prevents transcription by T. thermophilus RNAP from most host promoters. gp76 is less inhibitory for phage transcription, as tighter RNAP interaction with the phage promoters allows the template DNA to compete with gp76 for the common binding site. gp76 also inhibits Escherichia coli RNAP highlighting the template–DNA binding site as a new target site for developing antibacterial agents.