Biology subjects

Ebright, R. H.

Publications and source records attributed to Ebright, R. H..

At least 19 recordsLinked to original sources

bioRxiv2026

Single-molecule nanopore-tweezers analysis of transcription elongation by intact and "stalk-less" yeast RNA polymerase II

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 forces that assist or oppose translocation. Recently, we used SPRNT to analyze the translocation of single molecules of Escherichia coli RNA polymerase relative to the DNA template strand during transcription elongation, and we directly detected sequence-dependent pausing and formation of a "half-translocated state" at the E. coli yrbL consensus pause element. Here, we apply SPRNT to analyze the translocation of single molecules of yeast RNA polymerase II (Pol II) relative to the DNA template strand during transcription elongation with single-nucleotide spatial resolution and millisecond-scale temporal resolution at biologically relevant, saturating substrate concentrations; we compare translocation by intact, 12-subunit Pol II to translocation by a 10-subunit Pol II sub-assembly lacking the dissociable Rpb4-Rpb7 Pol II "stalk"; and we assess possible pausing by intact Pol II and stalk-less Pol II at the E. coli yrbL consensus pause element. The results show that intact Pol II elongates more rapidly than stalk-less Pol II and show that neither intact Pol II nor stalk-less Pol II pauses at the E. coli yrbL consensus pause element. One-sentence summaryNanopore tweezers enable monitoring of translocation of RNA polymerase II relative to DNA in transcription elongation with single-nucleotide spatial resolution and millisecond-scale temporal resolution at biologically relevant, saturating substrate concentrations.

molecular biology↗

bioRxiv2024

Structural basis of long-range transcription-translation coupling

Structures recently have been reported of molecular assemblies that mediate transcription-translation coupling in Escherichia coli. In these molecular assemblies, termed "coupled transcription-translation complexes" or "TTC-B", RNA polymerase (RNAP) directly interacts with the ribosome, the transcription elongation factor NusG or its paralog RfaH forms a bridge between RNAP and ribosome, and the transcription elongation factor NusA optionally forms a second bridge between RNAP and ribosome. Here, we report structures of coupled transcription-translation complexes having mRNA spacers between RNAP and ribosome longer than the maximum-length mRNA spacer compatible with formation of TTC-B. The results define a new class of coupled transcription-translation complex, termed "TTC-LC," where "LC" denotes "long-range coupling." TTC-LC differs from TTC-B by a [~]60{degrees} rotation and [~]70 [A] translation of RNAP relative to ribosome, resulting in loss of direct interactions between RNAP and ribosome and creation of a [~]70 [A] gap between RNAP and ribosome. TTC-LC accommodates long mRNA spacers by looping out mRNA from the gap between RNAP and ribosome. We present evidence that TTC-LC is an intermediate in assembling and disassembling TTC-B, mediating pre-TTC-B transcription-translation coupling before a ribosome catches up to RNAP, and mediating post-TTC-B transcription-translation coupling after a ribosome stops moving and RNAP continues moving. We show that TTC-B, but not TTC-LC, is severely defective in intrinsic, RNA-hairpin-dependent termination, and that both TTC-B and TTC-LC are severely defective in Rho-dependent termination.

molecular biology↗

bioRxiv2024

Structures of transcription-translation coupling complexes at each stage of the translation cycle

In the bacterium Escherichia coli, efficient expression of protein-coding genes is achieved through physical coupling of RNA polymerase (RNAP) synthesizing an mRNA and the first ribosome translating the mRNA, with transcription elongation factors NusG and NusA bridging RNAP and ribosome in a transcription-translation complex (TTC). Recent structural studies suggest that the flexibility in NusG and NusA accommodates the changes in ribosome conformation that occur during the translation cycle, but details have been unclear. Here, we report cryo-EM structures of TTCs at each stage of the translation cycle as an actively translating ribosome approaches to a halted transcription complex. We observe sequential conversion of a loosely coupled TTC (TTC-LC) to a tightly coupled TTC (TTC-B) to a collided TTC (TTC-A) as the ribosome approaches the transcription complex. We show that flexibility of the NusG linker and NusA "pantograph" enable TTC-LC and TTC-B to accommodate ribosome conformation at each stage of the translation cycle. We show that, in TTC-A, steric clash between ribosome and RNAP upon ribosome 30S head swiveling inhibits 30S head swiveling, consistent with translation slowdown, and applies mechanical force to the trailing edge of RNAP, causing transcription termination. Our results define the structures and properties of loosely coupled, tightly coupled, and collided TTCs at each stage of the translation cycle.

molecular biology↗

bioRxiv2023

Structural basis of RfaH-mediated transcription-translation coupling

The NusG paralog RfaH mediates bacterial transcription-translation coupling on genes that contain a DNA sequence element, termed an ops site, required for pausing RNA polymerase (RNAP) and for loading RfaH onto the paused RNAP. Here we report cryo-EM structures of transcription-translation complexes (TTCs) containing RfaH. The results show that RfaH bridges RNAP and the ribosome, with the RfaH N-terminal domain interacting with RNAP, and with the RfaH C-terminal domain interacting with the ribosome. The results show that the distribution of translational and orientational positions of RNAP relative to the ribosome in RfaH-coupled TTCs is more restricted than in NusG-coupled TTCs, due to the more restricted flexibility of the RfaH interdomain linker. The results further show that the structural organization of RfaH-coupled TTCs in the "loading state," in which RNAP and RfaH are located at the ops site during formation of the TTC, is the same as the structural organization of RfaH-coupled TTCs in the "loaded state," in which RNAP and RfaH are located at positions downstream of the ops site during function of the TTC. The results define the structural organization of RfaH-containing TTCs and set the stage for analysis of functions of RfaH during translation initiation and transcription-translation coupling. One sentence summaryCryo-EM reveals the structural basis of transcription-translation coupling by RfaH.

molecular biology↗

bioRxiv2023

Structural basis of archaeal FttA-dependent transcription termination

The ribonuclease FttA mediates factor-dependent transcription termination in archaea1-3. Here, we report the structure of a Thermococcus kodakarensis transcription pre-termination complex comprising FttA, Spt4, Spt5, and a transcription elongation complex (TEC). The structure shows that FttA interacts with the TEC in a manner that enables RNA to proceed directly from the TEC RNA-exit channel to the FttA catalytic center and that enables endonucleolytic cleavage of RNA by FttA, followed by 5[->]3 exonucleolytic cleavage of RNA by FttA and concomitant 5[->]3 translocation of FttA on RNA, to apply mechanical force to the TEC and trigger termination. The structure further reveals that Spt5 bridges FttA and the TEC, explaining how Spt5 stimulates FttA-dependent termination. The results reveal functional analogy between bacterial and archaeal factor-dependent termination, reveal functional homology between archaeal and eukaryotic factor-dependent termination, and reveal fundamental mechanistic similarities in factor-dependent termination in the three domains of life: bacterial, archaeal, and eukaryotic. One sentence summaryCryo-EM reveals the structure of the archaeal FttA pre-termination complex

molecular biology↗

bioRxiv2022

Identification and structural modeling of the chlamydial RNA polymerase omega subunit

Gene transcription in bacteria is carried out by the multisubunit RNA polymerase (RNAP), which is composed of a catalytic core enzyme and a promoter-recognizing {sigma} factor. RNAP core enzyme comprises two subunits, one {beta} subunit, one {beta} s subunit, and one {omega} (omega) subunit. Across multiple bacterial taxa, the RNAP {omega} subunit plays critical roles in the assembly of RNAP core enzyme and in other cellular functions, including regulation of bacterial growth, stress response, and biofilm formation. However, for several intracellular bacterium, including the obligate intracellular bacterium Chlamydia, no RNAP {omega} subunit previously has been identified. Here, we report the identification of Chlamydia trachomatis hypothetical protein CTL0286 as the chlamydial RNAP {omega} ortholog, based on sequence, synteny, and AlphaFold and AlphaFold-Multimer three-dimensional-structure predictions. We conclude that CTL0286 functions as the previously missing chlamydial {omega} ortholog. Extensions of our analysis indicate that all obligate intracellular bacteria have {omega} orthologs. IMPORTANCEChlamydiae are common mammalian pathogens. Chlamydiae have a unique developmental cycle characterized with an infectious but nondividing elementary body (EB), which can temporarily survive outside host cells, and a noninfectious reticulate body (RB), which replicates only intracellularly. Chlamydial development inside host cells can be arrested during persistence in response to adverse environmental conditions. Transcription plays a central role in the progression of the chlamydial developmental cycle as well as entry into and recovery from persistence. The identification of the elusive {omega} subunit of chlamydial RNAP makes possible future study of its regulatory roles in gene expression during chlamydial growth, development, and stress responses. This discovery also paves the way to prepare and study the intact chlamydial RNAP and its interactions with inhibitors in vitro.

molecular biology↗

bioRxiv2022

Structural basis of Rho-dependent transcription termination

Rho and NusG mediate factor-dependent transcription termination in Escherichia coli. Here, we report preparation of complexes functional in factor-dependent termination from RNA polymerase (RNAP), Rho, NusG, and synthetic nucleic-acid scaffolds, and we report cryo-EM structures of complexes. The structures show that functional factor-dependent pre-termination complexes contain a closed-ring Rho hexamer, have RNA threaded through the central channel of Rho, have 60 nt of RNA interacting sequence-specifically with the exterior of Rho and 6 nt of RNA interacting sequence-specifically with the central channel of Rho, have Rho oriented relative to RNAP such that ATP-hydrolysis-dependent translocation by Rho exerts mechanical force on RNAP, and have NusG bridging Rho and RNAP. The results explain five decades of research on Rho and provide a foundation for understanding Rho function. One sentence summaryCryo-EM reveals the structure of the functional Rho pre-termination complex

molecular biology↗

bioRxiv2022

Structural basis of transcription antitermination by Q{lambda}: NusA induces refolding of Q{lambda} to form nozzle for RNA polymerase exit channel

Lambdoid bacteriophage Q proteins are transcription antipausing and antitermination factors that enable RNA polymerase (RNAP) to read through pause and termination sites. Q proteins load onto RNAP engaged in promoter-proximal pausing at a Q binding element (QBE) and adjacent sigma-dependent pause element to yield a Q-loading complex, and translocate with RNAP as a pausing-deficient, termination-deficient Q-loaded complex. In previous work, we showed that the Q protein from bacteriophage 21 (Q21) functions by forming a "nozzle" that narrows and extends the RNAP RNA-exit channel, preventing formation of pause and termination RNA hairpins. Here, we report atomic structures of four states on the pathway of antitermination by the Q protein from bacteriophage {lambda} (Q{lambda}), a Q protein that shows no sequence similarity to Q21 and that, unlike Q21, requires the transcription elongation factor NusA for efficient antipausing and antitermination. We report structures of Q{lambda}, the Q{lambda}-QBE complex, the NusA-free "pre-engaged" Q{lambda}-loading complex, and the NusA-containing "engaged" Q{lambda}-loading complex. The results show that Q{lambda}, like Q21, forms a nozzle that narrows and extends the RNAP RNA-exit channel, preventing formation of RNA hairpins. However, the results show that Q{lambda} has no three-dimensional structural similarity to Q21, employs a different mechanism of QBE recognition than Q21, and employs a more complex process for loading onto RNAP than Q21, involving recruitment of Q{lambda} to form a "pre-engaged" loading complex, followed by NusA-facilitated refolding of Q{lambda} to form an "engaged" loading complex. The results establish Q{lambda} and Q21 are not structural homologs and are solely functional analogs. SIGNIFICANCE STATEMENTBacteriophage Q proteins are textbook examples of regulators of gene expression that function at the level of transcription antitermination. Here, we report structures defining the mechanism of antitermination by the Q protein of bacteriophage {lambda} (Q{lambda}). The results show Q{lambda} forms a "nozzle" that narrows and extends the RNA polymerase RNA-exit channel, precluding the formation of terminator RNA hairpins. The results show Q{lambda} exhibits no structural similarity to the Q protein of bacteriophage 21 (Q21), employs a different mechanism for DNA binding than Q21, and employs a more complex process of loading onto RNA polymerase than Q21. We conclude Q{lambda} and Q21 are not structural homologs and are solely functional analogs, akin to a bird wing and a bat wing.

molecular biology↗

bioRxiv2022

Structural and mechanistic basis of σ-dependent transcriptional pausing

In {sigma}-dependent transcriptional pausing, the transcription initiation factor {sigma}, translocating with RNA polymerase (RNAP), makes sequence-specific protein-DNA interactions with a promoter-like sequence element in the transcribed region, inducing pausing. It has been proposed that, in {sigma}-dependent pausing, the RNAP active center can access off-pathway "backtracked" states that are substrates for the transcript-cleavage factors of the Gre family, and on-pathway "scrunched" states that mediate pause escape. Here, using site-specific protein-DNA photocrosslinking to define positions of the RNAP trailing and leading edges and of {sigma} relative to DNA at the{lambda} PR promoter, we show directly that {sigma}-dependent pausing in the absence of GreB in vitro predominantly involves a state backtracked by 2-4 bp, and that {sigma}-dependent pausing in the presence of GreB in vitro and in vivo predominantly involves a state scrunched by 2-3 bp. Analogous experiments with a library of 47 ([~]16,000) transcribed-region sequences show that the state scrunched by 2-3 bp--and only that state--is associated with the consensus sequence, T-3N-2Y-1G+1, (where -1 corresponds to the position of the RNA 3 end), which is identical to the consensus for pausing in initial transcription, and which is related to the consensus for pausing in transcription elongation. Experiments with heteroduplex templates show that sequence information at position T-3 resides in the DNA nontemplate strand. A cryo-EM structure of a complex engaged in {sigma}-dependent pausing reveals positions of DNA scrunching on the DNA nontemplate and template strands and suggests that position T-3 of the consensus sequence exerts its effects by facilitating scrunching.

biochemistry↗

bioRxiv2021

Structural and mechanistic basis of RNA extension in reiterative transcription initiation: RNA slippingwithout DNA scrunching

Reiterative transcription initiation, observed at promoters that contain homopolymeric sequences at the transcription start site, generates RNA products having 5 sequences non-complementary to the DNA template. Here, using crystallography and cryo-EM to define structures, protein-DNA-photocrosslinking to map positions of RNAP leading and trailing edges relative to DNA, and single-molecule DNA nanomanipulation to assess RNAP-dependent DNA unwinding, we show that RNA extension in reiterative transcription initiation: (1) occurs without DNA scrunching, (2) involves a short, 2-3 bp RNA-DNA hybrid, and (3) generates RNA that exits RNAP through the portal by which scrunched nontemplate-strand DNA exits RNAP in standard transcription initiation. The results establish that, whereas RNA extension in standard transcription initiation proceeds through a scrunching mechanism, RNA extension in reiterative transcription initiation proceeds through a slippage mechanism, with slipping of RNA relative to DNA within a short RNA-DNA hybrid, and with extrusion of RNA from RNAP through an alternative RNA exit.

molecular biology↗

bioRxiv2021

Promoter-sequence determinants and structural basis of primer-dependent transcription initiation in Escherichia coli

Chemical modifications of RNA 5' ends enable "epitranscriptomic" regulation, influencing multiple aspects of RNA fate. In transcription initiation, a large inventory of substrates compete with nucleoside triphosphates (NTPs) for use as initiating entities, providing an ab initio mechanism for altering the RNA 5' end. In Escherichia coli cells, RNAs with a 5'-end hydroxyl are generated by use of dinucleotide RNAs as primers for transcription initiation, "primer-dependent initiation." Here we use massively systematic transcript end readout ("MASTER") to detect and quantify RNA 5' ends generated by primer-dependent initiation for ~410 (~1,000,000) promoter sequences in E. coli. The results show primer-dependent initiation in E. coli involves any of the 16 possible dinucleotide primers and depends on promoter sequences in, upstream, and downstream of the primer binding site. The results yield a consensus sequence for primer-dependent initiation, YTSS-2NTSS-1NTSSWTSS+1, where TSS is the transcription start site, NTSS-1NTSS is the primer binding site, Y is pyrimidine, and W is A or T. Biochemical and structure-determination studies show that the base pair (nontemplate-strand base:template-strand base) immediately upstream of the primer binding site (Y:RTSS-2, where R is purine) exerts its effect through the base on the DNA template strand (RTSS-2) through inter-chain base stacking with the RNA primer. Results from analysis of a large set of natural, chromosomally-encoded E. coli promoters support the conclusions from MASTER. Our findings provide a mechanistic and structural description of how TSS-region sequence hard-codes not only the TSS position, but also the potential for epitranscriptomic regulation through primer-dependent transcription initiation.

biochemistry↗

bioRxiv2021

Transcription initiation at a consensus bacterial promoter proceeds via a "bind-unwind-load-and-lock" mechanism

Transcription initiation starts with unwinding of promoter DNA by RNA polymerase (RNAP) to form a catalytically competent RNAP-promoter complex (RPO). Despite extensive study, the mechanism of promoter unwinding has remained unclear, in part due to the transient nature of intermediates on path to RPo. Here, using single-molecule unwinding-induced fluorescence enhancement to monitor promoter unwinding, and single-molecule fluorescence resonance energy transfer to monitor RNAP clamp conformation, we analyze RPo formation at a consensus bacterial core promoter. We find that the RNAP clamp is closed during promoter binding, remains closed during promoter unwinding, and then closes further, locking the unwound DNA in the RNAP active-centre cleft. Our work defines a new, "bind-unwind-load-and-lock," model for the series of conformational changes occurring during promoter unwinding at a consensus bacterial promoter and provides the tools needed to examine the process in other organisms and at other promoters. Significance statementTranscription initiation, the first step and most important step in gene expression for all organisms, involves unwinding of promoter DNA by RNA polymerase (RNAP) to form an open complex (RPo); this step also underpins transcriptional regulation and serves as an antibiotic target. Despite decades of research, the mechanism of promoter DNA unwinding has remained unresolved. Here, we solve this puzzle by using single-molecule fluorescence to directly monitor conformational changes in the promoter DNA and RNAP in real time during RPo formation. We show that RPo forms via a "bind-unwind-load-and-lock" mechanism, where the promoter unwinds outside the RNAP cleft, the unwound template DNA loads into the cleft, and RNAP "locks" the template DNA in place by closing the RNAP clamp module.

biochemistry↗

bioRxiv2020

Metabolomic investigation of the pseudouridimycin producer, a prolific streptomycete

We report a metabolomic analysis of Streptomyces sp. ID38640, a soil isolate that produces the bacterial RNA polymerase inhibitor pseudouridimycin. The analysis was performed on the wild type and on ten different pum mutants blocked at different steps in pseudouridimycin biosynthesis. The results indicate that Streptomyces sp. ID38640 is able to produce, in addition to pseudouridimcyin, lydicamycins and deferroxiamines, as previously reported, also the lassopeptide ulleungdin, the non-ribosomal peptide antipain and the osmoprotectant ectoine. The corresponding biosynthetic gene clusters were readily identified in the strain genome. We also detected the known compound pyridindolol, for which we propose a previously unreported biosynthetic gene cluster, as well as three families of unknown metabolites. Remarkably, the levels of the different metabolites varied strongly in the different mutant strains, allowing detection of metabolites not normally seen in the wild type. Three newly constructed pum mutants, along with systematic investigation of the accumulated metabolites, shed further lights on pseudouridimycin biosynthesis. We also show that several Streptomyces strains, harboring the pum biosynthetic gene cluster and unrelated to ID38640, readily produce pseudouridimycin.

microbiology↗

bioRxiv2020

RNA polymerase clamp conformational dynamics: long-lived states and modulation by crowding, cations, and nonspecific DNA binding

The RNA polymerase (RNAP) clamp, a mobile structural element conserved in RNAP from all domains of life, has been proposed to play critical roles at different stages of transcription. In previous work, we demonstrated using single-molecule Forster resonance energy transfer (smFRET) that RNAP clamp interconvert between three short-lived conformational states (lifetimes [~] 0.3-0.6 s), that the clamp can be locked into any one of these states by small molecules, and that the clamp stays closed during initial transcription and elongation. Here, we extend these studies to obtain a comprehensive understanding of clamp dynamics under conditions RNAP may encounter in living cells. We find that the RNAP clamp can populate long-lived conformational states (lifetimes >1.0 s) and can switch between these long-lived states and the previously observed short-lived states. In addition, we find that clamp motions are increased in the presence of molecular crowding, are unchanged in the presence of elevated monovalent-cation concentrations, and are reduced in the presence of elevated divalent-cation concentrations. Finally, we find that RNAP bound to non-specific DNA predominantly exhibits a closed clamp conformation. Our results raise the possibility of additional regulatory checkpoints that could affect clamp dynamics and consequently could affect transcription and transcriptional regulation.

biophysics↗

bioRxiv2020

Structural basis of transcription-translation coupling

In bacteria, transcription and translation are coupled processes, in which movement of RNA polymerase (RNAP) synthesizing mRNA is coordinated with movement of the first ribosome translating mRNA. Coupling is modulated by the transcription factors NusG--which is thought to bridge RNAP and ribosome--and NusA. Here, we report cryo-EM structures of Escherichia coli transcription-translation complexes (TTCs) containing different-length mRNA spacers between RNAP and the ribosome active-center P-site. Structures of TTCs containing short spacers show a state incompatible with NusG bridging and NusA binding (TTC-A; previously termed "expressome"). Structures of TTCs containing longer spacers reveal a new state compatible with NusG bridging and NusA binding (TTC-B) and reveal how NusG bridges and NusA binds. We propose that TTC-B mediates NusG- and NusA-dependent transcription-translation coupling. One Sentence SummaryCryo-EM defines states that mediate NusG- and NusA-dependent transcription-translation coupling in bacteria

molecular biology↗

bioRxiv2019

XACT-seq comprehensively defines the promoter-position and promoter-sequence determinants for initial-transcription pausing

Pausing by RNA polymerase (RNAP) during transcription elongation, in which a translocating RNAP uses a "stepping" mechanism, has been studied extensively, but pausing by RNAP during initial transcription, in which a promoter-anchored RNAP uses a "scrunching" mechanism, has not. We report a method that directly defines RNAP-active-center position relative to DNA in vivo with single-nucleotide resolution (XACT-seq; crosslink-between-active-center-and-template sequencing). We apply this method to detect and quantify pausing in initial transcription at 411 ([~]4,000,000) promoter sequences in vivo, in Escherichia coli. The results show initial-transcription pausing can occur in each nucleotide addition during initial transcription, particularly the first 4-5 nucleotide additions. The results further show initial-transcription pausing occurs at sequences that resemble the consensus sequence element for transcription-elongation pausing. Our findings define the positional and sequence determinants for initial-transcription pausing and establish initial-transcription pausing is hard-coded by sequence elements similar to those for transcription-elongation pausing.

biochemistry↗

bioRxiv2019

RNA extension drives a stepwise displacement of an initiation-factor structural module in initial transcription

All organisms--bacteria, archaea, and eukaryotes--have a transcription initiation factor that contains a structural module that binds within the RNA polymerase (RNAP) active-center cleft and interacts with template-strand single-stranded DNA (ssDNA) in the immediate vicinity of the RNAP active center. This transcription-initiation-factor structural module pre-organizes template-strand ssDNA to engage the RNAP active center, thereby facilitating binding of initiating nucleotides and enabling transcription initiation from initiating mononucleotides. However, this transcription-initiation-factor structural module occupies the path of nascent RNA and thus presumably must be displaced before or during initial transcription. Here, we report four sets of crystal structures of bacterial initially transcribing complexes that demonstrate, and define details of, stepwise, RNA-extension-driven displacement of the "{sigma} finger" of the bacterial transcription initiation factor {sigma}. The structures reveal that--for both the primary {sigma} factor and extracytoplasmic (ECF) {sigma} factors, and for both 5-triphosphate RNA and 5-hydroxy RNA--the "{sigma} finger" is displaced in stepwise fashion, progressively folding back upon itself, driven by collision with the RNA 5-end, upon extension of nascent RNA from [~]5 nt to [~]10 nt. SIGNIFICANCE STATEMENTThe "{sigma} finger" of the bacterial initiation factor {sigma} binds within the RNA polymerase active-center cleft and blocks the path of nascent RNA. It has been hypothesized that the {sigma} finger must be displaced during initial transcription. By determining crystal structures defining successive steps in initial transcription, we demonstrate that the {sigma} finger is displaced in stepwise fashion, driven by collision with the RNA 5-end, as nascent RNA is extended from [~]5 nt to [~]10 nt during initial transcription, and we show that this is true for both the primary {sigma} factor and alternate {sigma} factors. Stepwise displacement of the {sigma} finger can be conceptualized as stepwise compression of a "protein spring" that stores energy for subsequent breakage of protein-DNA and protein-protein interactions in promoter escape.

biochemistry↗

bioRxiv2019

Closing and opening of the RNA polymerase trigger loop

The RNA polymerase (RNAP) trigger loop (TL) is a mobile structural element of the RNAP active center that, based on crystal structures, has been proposed to cycle between an \"unfolded\"/\"open\" state that allows an NTP substrate to enter the active center and a \"folded\"/\"closed\" state that holds the NTP substrate in the active center. Here, by quantifying single-molecule fluorescence resonance energy transfer between a first fluorescent probe in the TL and a second fluorescent probe elsewhere in RNAP or in DNA, we detect and characterize TL closing and opening in solution. We show that the TL closes and opens on the millisecond timescale; we show that TL closing and opening provides a checkpoint for NTP complementarity, NTP ribo/deoxyribo identity, and NTP tri/di/monophosphate identity, and serves as a target for inhibitors; and we show that one cycle of TL closing and opening typically occurs in each nucleotide addition cycle in transcription elongation.

molecular biology↗