Insights into transcription: structure and function of single-subunit DNA-dependent RNA polymerases

Broccoli aptamer allows quantitative transcription regulation studies in vitro

Quantitative transcription regulation studies in vivo and in vitro often make use of reporter proteins. Here we show that using Broccoli aptamers, quantitative study of transcription in various regulatory scenarios is possible without a translational step. To explore the method we studied several regulatory scenarios that we analyzed using thermodynamic occupancy-based models, and found excellent agreement with previous studies. In the next step we show that non-coding DNA can have a dramatic effect on the level of transcription, similar to the influence of the lac repressor with a strong affinity to operator sites. Finally, we point out the limitations of the method in terms of delay times coupled to the folding of the aptamer. We conclude that the Broccoli aptamer is suitable for quantitative transcription measurements.

KSHV-encoded LANA bypasses transcriptional block through the stabilization of RNA Pol II in hypoxia

IMPORTANCE

Hypoxia can induce the reactivation of Kaposi sarcoma-associated virus (KSHV), which necessitates the synthesis of critical structural proteins. Despite the unfavorable energetic conditions of hypoxia, KSHV utilizes mechanisms to prevent the degradation of essential cellular machinery required for successful reactivation. Our study provides new insights on strategies employed by KSHV-infected cells to maintain steady-state transcription by overcoming hypoxia-mediated metabolic stress to enable successful reactivation. Our discovery that the interaction of latency-associated nuclear antigen with HIF1α and NEDD4 inhibits its polyubiquitination activity, which blocks the degradation of RNA Pol II during hypoxia, is a significant contribution to our understanding of KSHV biology. This newfound knowledge provides new leads in the development of novel therapies for KSHV-associated diseases.

RNA Pol II preferentially regulates ribosomal protein expression by trapping disassociated subunits

RNA polymerase II (RNA Pol II) has been recognized as a passively regulated multi-subunit holoenzyme. However, the extent to which RNA Pol II subunits might be important beyond the RNA Pol II complex remains unclear. Here, fractions containing disassociated RPB3 (dRPB3) were identified by size exclusion chromatography in various cells. Through a unique strategy, i.e., "specific degradation of disassociated subunits (SDDS)," we demonstrated that dRPB3 functions as a regulatory component of RNA Pol II to enable the preferential control of 3' end processing of ribosomal protein genes directly through its N-terminal domain. Machine learning analysis of large-scale genomic features revealed that the little elongation complex (LEC) helps to specialize the functions of dRPB3. Mechanistically, dRPB3 facilitates CBC-PCF11 axis activity to increase the efficiency of 3' end processing. Furthermore, RPB3 is dynamically regulated during development and diseases. These findings suggest that RNA Pol II gains specific regulatory functions by trapping disassociated subunits in mammalian cells.

The origin of genetic and metabolic systems: Evolutionary structuralinsights

DNA is derived from reverse transcription and its origin is related to reverse transcriptase, DNA polymerase and integrase. The gene structure originated from the evolution of the first RNA polymerase. Thus, an explanation of the origin of the genetic system must also explain the evolution of these enzymes. This paper proposes a polymer structure model, termed the stable complex evolution model, which explains the evolution of enzymes and functional molecules. Enzymes evolved their functions by forming locally tightly packed complexes with specific substrates. A metabolic reaction can therefore be considered to be the result of adaptive evolution in this way when a certain essential molecule is lacking in a cell. The evolution of the primitive genetic and metabolic systems was thus coordinated and synchronized. According to the stable complex model, almost all functional molecules establish binding affinity and specific recognition through complementary interactions, and functional molecules therefore have the nature of being auto-reactive. This is thermodynamically favorable and leads to functional duplication and self-organization. Therefore, it can be speculated that biological systems have a certain tendency to maintain functional stability or are influenced by an inherent selective power. The evolution of dormant bacteria may support this hypothesis, and inherent selectivity can be unified with natural selection at the molecular level.

Transcriptomics-Driven Characterization of LUZ100, a T7-like Pseudomonas Phage with Temperate Features

Autographiviridae is a diverse yet distinct family of bacterial viruses marked by a strictly lytic lifestyle and a generally conserved genome organization. Here, we characterized Pseudomonas aeruginosa phage LUZ100, a distant relative of type phage T7. LUZ100 is a podovirus with a limited host range which likely uses lipopolysaccharide (LPS) as a phage receptor. Interestingly, infection dynamics of LUZ100 indicated moderate adsorption rates and low virulence, hinting at temperate characteristics. This hypothesis was supported by genomic analysis, which showed that LUZ100 shares the conventional T7-like genome organization yet carries key genes associated with a temperate lifestyle. To unravel the peculiar characteristics of LUZ100, ONT-cappable-seq transcriptomics analysis was performed. These data provided a bird's-eye view of the LUZ100 transcriptome and enabled the discovery of key regulatory elements, antisense RNA, and transcriptional unit structures. The transcriptional map of LUZ100 also allowed us to identify new RNA polymerase (RNAP)-promoter pairs that can form the basis for biotechnological parts and tools for new synthetic transcription regulation circuitry. The ONT-cappable-seq data revealed that the LUZ100 integrase and a MarR-like regulator (proposed to be involved in the lytic/lysogeny decision) are actively cotranscribed in an operon. In addition, the presence of a phage-specific promoter transcribing the phage-encoded RNA polymerase raises questions on the regulation of this polymerase and suggests that it is interwoven with the MarR-based regulation. This transcriptomics-driven characterization of LUZ100 supports recent evidence that T7-like phages should not automatically be assumed to have a strictly lytic life cycle. IMPORTANCE Bacteriophage T7, considered the "model phage" of the Autographiviridae family, is marked by a strictly lytic life cycle and conserved genome organization. Recently, novel phages within this clade have emerged which display characteristics associated with a temperate life cycle. Screening for temperate behavior is of utmost importance in fields like phage therapy, where strictly lytic phages are generally required for therapeutic applications. In this study, we applied an omics-driven approach to characterize the T7-like Pseudomonas aeruginosa phage LUZ100. These results led to the identification of actively transcribed lysogeny-associated genes in the phage genome, pointing out that temperate T7-like phages are emerging more frequent than initially thought. In short, the combination of genomics and transcriptomics allowed us to obtain a better understanding of the biology of nonmodel Autographiviridae phages, which can be used to optimize the implementation of phages and their regulatory elements in phage therapy and biotechnological applications, respectively.

pH modulates the role of SP6 RNA polymerase in transcription process: an in silico study

SP6 RNA polymerase (SP6 RNAP) is an essential enzyme for the transcription process in SP6 bacteriophage. SP6 RNAP plays a vital role in mRNA vaccine designing technology and other translational biotechnology research due to the high specificity towards its promoter. The self-replicating performance also put this polymerase to study extensively. Despite of the reports emphasizing the function of this enzyme, a detailed structural and functional understanding of RNA polymerase is not reported so far. Here, we report the first-ever information about SP6RNAP structure and its effect on promoter binding at different pH environments using molecular docking and molecular dynamics simulation (MDS) study. We also report the changes in polymerase conformations in different pH conditions using in-silico approach. The docking study was also performed for SP6 RNAP with SP6 promoter at different pH environments using the in-silico docking tools and conducted the MDS study for complexes. MM/PBSA and per residue energy contribution has been performed at three different pH environments. The structural aspects confirmed that the pH 7.9 state favors the polymerase functional activity in the transcription process which was in the range reported using transcription assay. This polymerase's unique features may play its emerging role as an efficient transcription factor in translational biological research.Communicated by Ramaswamy H. Sarma.

Recruitment of Mobile Genetic Elements for Diverse Cellular Functions in Prokaryotes

Prokaryotic genomes are replete with mobile genetic elements (MGE) that span a continuum of replication autonomy. On numerous occasions during microbial evolution, diverse MGE lose their autonomy altogether but, rather than being quickly purged from the host genome, assume a new function that benefits the host, rendering the immobilized MGE subject to purifying selection, and resulting in its vertical inheritance. This mini-review highlights the diversity of the repurposed (exapted) MGE as well as the plethora of cellular functions that they perform. The principal contribution of the exaptation of MGE and their components is to the prokaryotic functional systems involved in biological conflicts, and in particular, defense against viruses and other MGE. This evolutionary entanglement between MGE and defense systems appears to stem both from mechanistic similarities and from similar evolutionary predicaments whereby both MGEs and defense systems tend to incur fitness costs to the hosts and thereby evolve mechanisms for survival including horizontal mobility, causing host addiction, and exaptation for functions beneficial to the host. The examples discussed demonstrate that the identity of an MGE, overall mobility and relationship with the host cell (mutualistic, symbiotic, commensal, or parasitic) are all factors that affect exaptation.

Method for Rapid Analysis of Mutant RNA Polymerase Activity on Templates Containing Unnatural Nucleotides

Pairs of unnatural nucleotides are used to expand the genetic code and create artificial DNA or RNA templates. In general, an approach is used to engineer orthogonal systems capable of reading codons comprising artificial nucleotides; however, DNA and RNA polymerases capable of recognizing unnatural nucleotides are required for amplification and transcription of templates. Under favorable conditions, in the presence of modified nucleotide triphosphates, DNA polymerases are able to synthesize unnatural DNA with high efficiency; however, the currently available RNA polymerases reveal high specificity to the natural nucleotides and may not easily recognize the unnatural nucleotides. Due to the absence of simple and rapid methods for testing the activity of mutant RNA polymerases, the development of RNA polymerase recognizing unnatural nucleotides is limited. To fill this gap, we developed a method for rapid analysis of mutant RNA polymerase activity on templates containing unnatural nucleotides. Herein, we optimized a coupled cell-free translation system and tested the ability of three unnatural nucleotides to be transcribed by different T7 RNA polymerase mutants, by demonstrating high sensitivity and simplicity of the developed method. This approach can be applied to various unnatural nucleotides and can be simultaneously scaled up to determine the activity of numerous polymerases on different templates. Due to the simplicity and small amounts of material required, the developed cell-free system provides a highly scalable and versatile tool to study RNA polymerase activity.

Structural Insights into the Respiratory Syncytial Virus RNA Synthesis Complexes

RNA synthesis in respiratory syncytial virus (RSV), a negative-sense (-) nonsegmented RNA virus, consists of viral gene transcription and genome replication. Gene transcription includes the positive-sense (+) viral mRNA synthesis, 5'-RNA capping and methylation, and 3' end polyadenylation. Genome replication includes (+) RNA antigenome and (-) RNA genome synthesis. RSV executes the viral RNA synthesis using an RNA synthesis ribonucleoprotein (RNP) complex, comprising four proteins, the nucleoprotein (N), the large protein (L), the phosphoprotein (P), and the M2-1 protein. We provide an overview of the RSV RNA synthesis and the structural insights into the RSV gene transcription and genome replication process. We propose a model of how the essential four proteins coordinate their activities in different RNA synthesis processes.

Evidence for a role of phenotypic mutations in virus adaptation

Viruses interact extensively with the host molecular machinery, but the underlying mechanisms are poorly understood. Bacteriophage T7 recruits the small protein thioredoxin of the Escherichia coli host as an essential processivity factor for the viral DNA polymerase. We challenged the phage to propagate in a host in which thioredoxin had been extensively modified to hamper its recruitment. The virus adapted to the engineered host without losing the capability to propagate in the original host, but no genetic mutations were fixed in the thioredoxin binding domain of the viral DNA polymerase. Virus adaptation correlated with mutations in the viral RNA polymerase, supporting that promiscuous thioredoxin recruitment was enabled by phenotypic mutations caused by transcription errors. These results point to a mechanism of virus adaptation that may play a role in cross-species transmission. We propose that phenotypic mutations may generally contribute to the capability of viruses to evade antiviral strategies.

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Phage adapts to a host modified to hinder the essential recruitment of a host protein

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No genetic mutations are fixed at the engineered virus-host interaction interface

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Adaptation is likely linked to phenotypic mutations caused by transcription errors

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Sub-genomic RNAs may enable this kind of adaptation mechanism in coronaviruses

Cryo-EM Structures Reveal Transcription Initiation Steps by Yeast Mitochondrial RNA Polymerase

Mitochondrial RNA polymerase (mtRNAP) is crucial in cellular energy production, yet understanding of mitochondrial DNA transcription initiation lags that of bacterial and nuclear DNA transcription. We report structures of two transcription initiation intermediate states of yeast mtRNAP that explain promoter melting, template alignment, DNA scrunching, abortive synthesis, and transition into elongation. In the partially melted initiation complex (PmIC), transcription factor MTF1 makes base-specific interactions with flipped non-template (NT) nucleotides "AAGT" at -4 to -1 positions of the DNA promoter. In the initiation complex (IC), the template in the expanded 7-mer bubble positions the RNA and NTP analog UTPαS, while NT scrunches into an NT loop. The scrunched NT loop is stabilized by the centrally positioned MTF1 C-tail. The IC and PmIC states coexist in solution, revealing a dynamic equilibrium between two functional states. Frequent scrunching/unscruching transitions and the imminent steric clashes of the inflating NT loop and growing RNA:DNA with the C-tail explain abortive synthesis and transition into elongation.

Interference of dengue replication by blocking the access of 3' SL RNA to the viral RNA-dependent RNA polymerase

The four circulating serotypes of dengue virus (DENV) occasionally cause potentially fetal symptoms of severe dengue, which there is currently no specific treatment available. Extensive efforts have been made to inhibit viral replication processes by impeding the activity of an exclusive RNA-dependent RNA polymerase (RdRp) in the viral non-structural protein 5 (NS5). In our earlier work, we identified the characteristic, specific interaction between the C-terminal thumb subdomain of RdRp and an apical loop in the 3' stem-loop (SL) element in the DENV RNA genome, which is fundamental for viral replication. Here, we demonstrated a new approach for interfering viral replication via blocking of 3' SL RNA binding to RdRp by the single-chain variable fragments (scFvs). We isolated and cloned 3 different human scFvs that bound to RdRp from DENV serotype 2 and interfered with 3' SL-binding, utilizing a combination of phage-display panning and Alpha methods. When tagged with a cell penetrating peptide, a selected scFv clone, 2E3, entered cells and partially colocalized with NS5 in the cytoplasm of infected HuH-7 cells. 2E3 significantly inhibited DENV RNA replication with sub-nanomolar EC50 values and significantly reduced the production of infectious particles. The molecular docking models suggested that 2E3 recognized both palm and thumb subdomains of RdRp, and interacted with Lys⁸⁴¹, a key residue involved in RNA binding. Our results provide a new potential therapeutic molecule specific for flaviviral infection.

The replication machinery of LUCA: common origin of DNA replication and transcription

Origin of DNA replication is an enigma because the replicative DNA polymerases (DNAPs) are not homologous among the three domains of life, Bacteria, Archaea, and Eukarya. The homology between the archaeal replicative DNAP (PolD) and the large subunits of the universal RNA polymerase (RNAP) responsible for transcription suggests a parsimonious evolutionary scenario. Under this model, RNAPs and replicative DNAPs evolved from a common ancestor that functioned as an RNA-dependent RNA polymerase in the RNA-protein world that predated the advent of DNA replication. The replicative DNAP of the Last Universal Cellular Ancestor (LUCA) would be the ancestor of the archaeal PolD.

Promoter Length Affects the Initiation of T7 RNA Polymerase In Vitro: New Insights into Promoter/Polymerase Co-evolution

Polymerases are integral factors of gene expression and are essential for the maintenance and transmission of genetic information. RNA polymerases (RNAPs) differ from other polymerases in that they can bind promoter sequences and initiate transcription de novo and this promoter recognition requires the presence of specific DNA binding domains in the polymerase. Bacteriophage T7 RNA polymerase (T7RNAP) is the prototype for single subunit RNA polymerases which include bacteriophage and mitochondrial RNAPs, and the structure and mechanistic aspects of transcription by T7 RNAP are well characterized. Here, we describe experiments to determine whether the prototype T7 RNAP is able to recognize and initiate at truncated promoters similar to mitochondrial promoters. Using an in vitro oligonucleotide transcriptional system, we have assayed transcription initiation activity by T7 RNAP. These assays have not only defined the limits of conventional de novo initiation on truncated promoters, but have identified novel activities of initiation of RNA synthesis. We propose that these novel activities may be vestigial activities surviving from the transition of single subunit polymerase initiation using primers to de novo initiation using promoters.

Structure and Function of RNA Polymerases and the Transcription Machineries

In all living organisms, the flow of genetic information is a two-step process: first DNA is transcribed into RNA, which is subsequently used as template for protein synthesis during translation. In bacteria, archaea and eukaryotes, transcription is carried out by multi-subunit RNA polymerases (RNAPs) sharing a conserved architecture of the RNAP core. RNAPs catalyse the highly accurate polymerisation of RNA from NTP building blocks, utilising DNA as template, being assisted by transcription factors during the initiation, elongation and termination phase of transcription. The complexity of this highly dynamic process is reflected in the intricate network of protein-protein and protein-nucleic acid interactions in transcription complexes and the substantial conformational changes of the RNAP as it progresses through the transcription cycle.In this chapter, we will first briefly describe the early work that led to the discovery of multisubunit RNAPs. We will then discuss the three-dimensional organisation of RNAPs from the bacterial, archaeal and eukaryotic domains of life, highlighting the conserved nature, but also the domain-specific features of the transcriptional apparatus. Another section will focus on transcription factors and their role in regulating the RNA polymerase throughout the different phases of the transcription cycle. This includes a discussion of the molecular mechanisms and dynamic events that govern transcription initiation, elongation and termination.

Dual coding potential of a 2',5'-branched ribonucleotide in DNA

Branchpoints in RNA templates are highly mutagenic, but it is not known yet whether this also applies to branchpoints in DNA templates. Here, we report how nucleic acid polymerases replicate a 2',5'-branched DNA (bDNA) molecule. We constructed long-chained bDNA templates containing a branch guanosine and T7 promoters at both arms by splinted ligation. Quantitative real-time PCR analysis was used to investigate whether a branchpoint blocks DNA synthesis from the two arms in the same manner. We find that the blocking effect of a branchpoint is arm-specific. DNA synthesis from the 2'-arm is more than 20,000-fold decreased, whereas from the 3'-arm only 15-fold. Our sequence analysis of full-length nucleic acid generated by Taq DNA polymerase, Moloney murine leukemia virus reverse transcriptase, and T7 RNA polymerase from the 2'-arm of bDNA shows that the branched guanine has a dual coding potential and can base-pair with cytosine and guanine. We find that branchpoint templating is influenced by the type of the surrounding nucleic acid and is probably modulated by polymerase and RNase H active sites. We show that the branchpoint bypass by the polymerases from the 3'-arm of bDNA is predominantly error-free, indicating that bDNA is not as highly mutagenic as 2',5'-branched RNA.

Unusual relatives of the multisubunit RNA polymerase

Transcription, the first step of gene expression, is accomplished in all domains of life by the multisubunit RNA polymerase (msRNAP). Accordingly, the msRNAP is an ancient enzyme that is ubiquitous across all cellular organisms. Conserved in absolutely all msRNAPs is the catalytic magnesium-binding aspartate triad and the structural fold it is present on, the double ψ β barrel (DPBB). In-depth bioinformatics has begun to reveal a wealth of unusual proteins distantly related to msRNAP, identified due to their possession of the aspartate triad and DPBB folds. Three examples of these novel RNAPs are YonO of the Bacillus subtilis SPβ prophage, non-virion RNAP (nvRNAP) of the B. subtilis AR9 bacteriophage and ORF6 RNAP of the Kluyveromyces lactis cytoplasmic killer system. While YonO and AR9 nvRNAP are both bacteriophage enzymes, they drastically contrast. YonO is an incredibly minimal single-subunit RNAP, while AR9 nvRNAP is multisubunit bearing much more resemblance to the canonical msRNAP. ORF6 RNAP is an intermediate, given it is a single-subunit enzyme with substantial conservation with the msRNAP. Recent findings have begun to shed light on these polymerases, which have the potential to update our understanding of the mechanisms used for transcription and give new insights into the canonical msRNAP and its evolution. This mini-review serves to introduce and outline our current understanding of these three examples of novel, unusual RNAPs.

Highly efficient 5' capping of mitochondrial RNA with NAD+ and NADH by yeast and human mitochondrial RNA polymerase

Bacterial and eukaryotic nuclear RNA polymerases (RNAPs) cap RNA with the oxidized and reduced forms of the metabolic effector nicotinamide adenine dinucleotide, NAD⁺ and NADH, using NAD⁺ and NADH as non-canonical initiating nucleotides for transcription initiation. Here, we show that mitochondrial RNAPs (mtRNAPs) cap RNA with NAD⁺ and NADH, and do so more efficiently than nuclear RNAPs. Direct quantitation of NAD⁺- and NADH-capped RNA demonstrates remarkably high levels of capping in vivo: up to ~60% NAD⁺ and NADH capping of yeast mitochondrial transcripts, and up to ~15% NAD⁺ capping of human mitochondrial transcripts. The capping efficiency is determined by promoter sequence at, and upstream of, the transcription start site and, in yeast and human cells, by intracellular NAD⁺ and NADH levels. Our findings indicate mtRNAPs serve as both sensors and actuators in coupling cellular metabolism to mitochondrial transcriptional outputs, sensing NAD⁺ and NADH levels and adjusting transcriptional outputs accordingly.

Minimalism and functionality: Structural lessons from the heterodimeric N4 bacteriophage RNA polymerase II

Genomes of phages, mitochondria, and chloroplasts are transcribed by a diverse group of transcriptional machineries with structurally related single-subunit RNA polymerases (RNAPs). Our understanding of transcription mechanisms of these enzymes is predominantly based on biochemical and structural studies of three most-studied members, transcription factor-independent phage T7 RNAP, transcription factor-dependent phage N4 virion-encapsidated RNAP, and transcription factor-dependent mitochondrial RNAPs (mtRNAP). Although these RNAPs employ completely different mechanisms for promoter recognition and transcription termination, these enzymes are relatively large and formed by single polypeptides. Historically being a model enzyme for studying the mechanisms of transcription by T7-like RNAPs, however, T7 RNAP represents only a small group of RNAPs in this family. The vast majority of T7-like RNAPs are transcription factor-dependent, and several of them are heterodimeric enzymes. Here, we report X-ray crystal structures of transcription complexes of the smallest and heterodimeric form of T7-like RNAP, bacteriophage N4 RNAPII, providing insights into the structural organization of a minimum RNAP in this family. We analyze structural and functional aspects of heterodimeric architecture of N4 RNAPII concerning the mechanisms of transcription initiation and transition to processive RNA elongation. Interestingly, N4 RNAPII maintains the same conformation in promoter-bound and elongation transcription complexes, revealing a novel transcription mechanism for single-subunit RNAPs. This work establishes a structural basis for studying mechanistic aspects of transcription by factor-dependent minimum RNAP.

Taxon Richness of "Megaviridae" Exceeds those of Bacteria and Archaea in the Ocean

Since the discovery of the giant mimivirus, evolutionarily related viruses have been isolated or identified from various environments. Phylogenetic analyses of this group of viruses, tentatively referred to as the family “Megaviridae”, suggest that it has an ancient origin that may predate the emergence of major eukaryotic lineages. Environmental genomics has since revealed that Megaviridae represents one of the most abundant and diverse groups of viruses in the ocean. In the present study, we compared the taxon richness and phylogenetic diversity of Megaviridae, Bacteria, and Archaea using DNA-dependent RNA polymerase as a common marker gene. By leveraging existing microbial metagenomic data, we found higher richness and phylogenetic diversity in this single viral family than in the two prokaryotic domains. We also obtained results showing that the evolutionary rate alone cannot account for the observed high diversity of Megaviridae lineages. These results suggest that the Megaviridae family has a deep co-evolutionary history with diverse marine protists since the early “Big-Bang” radiation of the eukaryotic tree of life.

Deep-sea vent phage DNA polymerase specifically initiates DNA synthesis in the absence of primers

A DNA polymerase is encoded by the deep-sea vent phage NrS-1. NrS-1 has a unique genome organization containing genes that are predicted to encode a helicase and a single-stranded DNA (ssDNA)-binding protein. The gene for an unknown protein shares weak homology with the bifunctional primase-polymerases (prim-pols) from archaeal plasmids but is missing the zinc-binding domain typically found in primases. We show that this gene product has efficient DNA polymerase activity and is processive in DNA synthesis in the presence of the NrS-1 helicase and ssDNA-binding protein. Remarkably, this NrS-1 DNA polymerase initiates DNA synthesis from a specific template DNA sequence in the absence of any primer. The de novo DNA polymerase activity resides in the N-terminal domain of the protein, whereas the C-terminal domain enhances DNA binding.

Regulation of infection efficiency in a globally abundant marine Bacteriodetes virus

Bacteria impact humans, industry and nature, but do so under viral constraints. Problematically, knowledge of viral infection efficiencies and outcomes derives from few model systems that over-represent efficient lytic infections and under-represent virus-host natural diversity. Here we sought to understand infection efficiency regulation in an emerging environmental Bacteroidetes-virus model system with markedly different outcomes on two genetically and physiologically nearly identical host strains. For this, we quantified bacterial virus (phage) and host DNA, transcripts and phage particles throughout both infections. While phage transcriptomes were similar, transcriptional differences between hosts suggested host-derived regulation of infection efficiency. Specifically, the alternative host overexpressed DNA degradation genes and underexpressed translation genes, which seemingly targeted phage DNA particle production, as experiments revealed they were both significantly delayed (by >30 min) and reduced (by >50%) in the inefficient infection. This suggests phage failure to repress early alternative host expression and stress response allowed the host to respond against infection by delaying phage DNA replication and protein translation. Given that this phage type is ubiquitous and abundant in the global oceans and that variable viral infection efficiencies are central to dynamic ecosystems, these data provide a critically needed foundation for understanding and modeling viral infections in nature.

Interaction Analysis of T7 RNA Polymerase with Heparin and Its Low Molecular Weight Derivatives - An In Silico Approach

The single subunit T7 RNA polymerase (T7RNAP) is a model enzyme for studying the transcription process and for various biochemical and biophysical studies. Heparin is a commonly used inhibitor against T7RNAP and other RNA polymerases. However, exact interaction between heparin and T7RNAP is still not completely understood. In this work, we analyzed the binding pattern of heparin by docking heparin and few of its low molecular weight derivatives to T7RNAP, which helps in better understanding of T7RNAP inhibition mechanism. The efficiency of the compounds was calculated by docking the selected compounds and post-docking molecular mechanics/generalized Born surface area analysis. Evaluation of the simulation trajectories and binding free energies of the complexes after simulation showed enoxaparin to be the best among low molecular weight heparins. Binding free energy analysis revealed that van der Waals interactions and polar solvation energy provided the substantial driving force for the binding process. Furthermore, per-residue free energy decomposition analysis revealed that the residues Asp 471, Asp 506, Asp 537, Tyr 571, Met 635, Asp 653, Pro 780, and Asp 812 are important for heparin interaction. Apart from these residues, most favorable contribution in all the three complexes came from Asp 506, Tyr 571, Met 635, Glu 652, and Asp 653, which can be essential for binding of heparin-like structures with T7RNAP. The results obtained from this study will be valuable for the future rational design of novel and potent inhibitors against T7RNAP and related proteins.

Inorganic nanolayers: structure, preparation, and biomedical applications

Hydrotalcite-like compounds are two-dimensional inorganic nanolayers also known as clay minerals or anionic clays or layered double hydroxides/layered hydroxy salts, and have emerged as a single type of material with numerous biomedical applications, such as drug delivery, gene delivery, cosmetics, and biosensing. Inorganic nanolayers are promising materials due to their fascinating properties, such as ease of preparation, ability to intercalate different type of anions (inorganic, organic, biomolecules, and even genes), high thermal stability, delivery of intercalated anions in a sustained manner, high biocompatibility, and easy biodegradation. Inorganic nanolayers have been the focus for researchers over the last decade, resulting in widening application horizons, especially in the field of biomedical science. These nanolayers have been widely applied in drug and gene delivery. They have also been applied in biosensing technology, and most recently in bioimaging science. The suitability of inorganic nanolayers for application in drug delivery, gene delivery, biosensing technology, and bioimaging science makes them ideal materials to be applied for theranostic purposes. In this paper, we review the structure, methods of preparation, and latest advances made by inorganic nanolayers in such biomedical applications as drug delivery, gene delivery, biosensing, and bioimaging.

A suggested new bacteriophage genus, "Kp34likevirus", within the Autographivirinae subfamily of Podoviridae

Klebsiella pneumoniae phages vB_KpnP_SU503 (SU503) and vB_KpnP_SU552A (SU552A) are virulent viruses belonging to the Autographivirinae subfamily of Podoviridae that infect and kill multi-resistant K. pneumoniae isolates. Phages SU503 and SU552A show high pairwise nucleotide identity to Klebsiella phages KP34 (NC_013649), F19 (NC_023567) and NTUH-K2044-K1-1 (NC_025418). Bioinformatic analysis of these phage genomes show high conservation of gene arrangement and gene content, conserved catalytically active residues of their RNA polymerase, a common and specific lysis cassette, and form a joint cluster in phylogenetic analysis of their conserved genes. Also, we have performed biological characterization of the burst size, latent period, host specificity (together with KP34 and NTUH-K2044-K1-1), morphology, and structural genes as well as sensitivity testing to various conditions. Based on the analyses of these phages, the creation of a new phage genus is suggested within the Autographivirinae, called "Kp34likevirus" after their type phage, KP34. This genus should encompass the recently genome sequenced Klebsiella phages KP34, SU503, SU552A, F19 and NTUH-K2044-K1-1.

Synthetic biology outside the cell: linking computational tools to cell-free systems

As mathematical models become more commonly integrated into the study of biology, a common language for describing biological processes is manifesting. Many tools have emerged for the simulation of in vivo synthetic biological systems, with only a few examples of prominent work done on predicting the dynamics of cell-free synthetic systems. At the same time, experimental biologists have begun to study dynamics of in vitro systems encapsulated by amphiphilic molecules, opening the door for the development of a new generation of biomimetic systems. In this review, we explore both in vivo and in vitro models of biochemical networks with a special focus on tools that could be applied to the construction of cell-free expression systems. We believe that quantitative studies of complex cellular mechanisms and pathways in synthetic systems can yield important insights into what makes cells different from conventional chemical systems.

Yeast mitochondrial RNAP conformational changes are regulated by interactions with the mitochondrial transcription factor

Mitochondrial RNA polymerases (MtRNAPs) are members of the single-subunit RNAP family, the most well-characterized member being the RNAP from T7 bacteriophage. MtRNAPs are, however, functionally distinct in that they depend on one or more transcription factors to recognize and open the promoter and initiate transcription, while the phage RNAPs are capable of performing these tasks alone. Since the transcriptional mechanisms that are conserved in phage and mitochondrial RNAPs have been so effectively characterized in the phage enzymes, outstanding structure-mechanism questions concern those aspects that are distinct in the MtRNAPs, particularly the role of the mitochondrial transcription factor(s). To address these questions we have used both negative staining and cryo-EM to generate three-dimensional reconstructions of yeast MtRNAP initiation complexes with and without the mitochondrial transcription factor (MTF1), and of the elongation complex. Together with biochemical experiments, these data indicate that MTF1 uses multiple mechanisms to drive promoter opening, and that its interactions with the MtRNAP regulate the conformational changes undergone by the latter enzyme as it traverses the template strand.

Fluorescent methods to study transcription initiation and transition into elongation

The DNA-dependent RNA polymerases induce specific conformational changes in the promoter DNA during transcription initiation. Fluorescence spectroscopy sensitively monitors these DNA conformational changes in real time and at equilibrium providing powerful ways to estimate interactions in transcriptional complexes and to assess how transcription is regulated by the promoter DNA sequence, transcription factors, and small ligands. Ensemble fluorescence methods described here probe the individual steps of promoter binding, bending, opening, and transition into the elongation using T7 phage and mitochondrial transcriptional systems as examples.

Preparation and antibacterial activity of lysozyme and layered double hydroxide nanocomposites

It is necessary to develop "green" disinfection technology which does not produce disinfection by-products. Lysozyme-layered double hydroxide nanocomposites (LYZ-LDHs) were prepared by intercalating LYZ in LDH for the first time. Their antibacterial activity was evaluated using staphylococcus aureus as a target. The bacteria removal mechanism was also studied. Characterization of LYZ-LDHs by X-ray diffraction and Fourier transform infrared spectroscopy indicated that LYZ was successfully intercalated in LDH, compressed and deformed without secondary structural change. LYZ-LDHs showed excellent bactericidal effectiveness against staphylococcus aureus. The antibacterial performance of LYZ-LDHs was found to be affected by the LYZ/LDH ratio and the pH of the bacteria-containing water. The bacteria removal efficiency of LYZ-LDHs with LYZ/LDH mass ratio of 0.8 was consistently above 94% over the pH range of 3-9. LYZ-LDHs adsorbed bacteria to their surface by LDH and then killed them by the immobilized LYZ. This new material integrated the bactericidal ability of LYZ and adsorption ability of LDH. Moreover, the antibacterial ability of LYZ-LDHs was persistent and not limited by the adsorption capacity.

An update on the molecular genetics toolbox for staphylococci

Staphylococci are Gram-positive spherical bacteria of enormous clinical and biotechnological relevance. Staphylococcus aureus has been extensively studied as a model pathogen. A plethora of methods and molecular tools has been developed for genetic modification of at least ten different staphylococcal species to date. Here we review recent developments of various genetic tools and molecular methods for staphylococcal research, which include reporter systems and vectors for controllable gene expression, gene inactivation, gene essentiality testing, chromosomal integration and transposon delivery. It is furthermore illustrated how mutant strain construction by homologous or site-specific recombination benefits from sophisticated counterselection methods. The underlying genetic components have been shown to operate in wild-type staphylococci or modified chassis strains. Finally, possible future developments in the field of applied Staphylococcus genetics are highlighted.

Effects of cytosine hydroxymethylation on DNA strand separation

Cytosine hydroxymethylation is an epigenetic control factor in higher organisms. New discoveries of the biological roles of hydroxymethylation serve to raise questions about how this epigenetic modification exerts its functions and how organisms discriminate cytosine hydroxymethylation from methylation. Here, we report investigations that reveal an effect of cytosine hydroxymethylation on mechanical properties of DNA under load. The findings are based on molecular force assay measurements and steered molecular dynamics simulations. Molecular force assay experiments identified significant effects of hydroxymethylation on stretching-induced strand separation; the underlying physical mechanism has been revealed by steered molecular dynamics simulations. We find that hydroxymethylation can either upregulate or downregulate DNA's strand separation propensity, suggesting that hydroxymethylation can control gene expression by facilitating or obstructing the action of transcription machinery or the access to chromosomal DNA.

The RNA polymerase of marine cyanophage Syn5

A single subunit DNA-dependent RNA polymerase was identified and purified to apparent homogeneity from cyanophage Syn5 that infects the marine cyanobacteria Synechococcus. Syn5 is homologous to bacteriophage T7 that infects Escherichia coli. Using the purified enzyme its promoter has been identified by examining transcription of segments of Syn5 DNA and sequencing the 5'-termini of the transcripts. Only two Syn5 RNAP promoters, having the sequence 5'-ATTGGGCACCCGTAA-3', are found within the Syn5 genome. One promoter is located within the Syn5 RNA polymerase gene and the other is located close to the right genetic end of the genome. The purified enzyme and its promoter have enabled a determination of the requirements for transcription. Unlike the salt-sensitive bacteriophage T7 RNA polymerase, this marine RNA polymerase requires 160 mm potassium for maximal activity. The optimal temperature for Syn5 RNA polymerase is 24 °C, much lower than that for T7 RNA polymerase. Magnesium is required as a cofactor although some activity is observed with ferrous ions. Syn5 RNA polymerase is more efficient in utilizing low concentrations of ribonucleotides than T7 RNA polymerase.

A nexus for gene expression-molecular mechanisms of Spt5 and NusG in the three domains of life

Evolutionary related multisubunit RNA polymerases (RNAPs) transcribe the genomes of all living organisms. Whereas the core subunits of RNAPs are universally conserved in all three domains of life—indicative of a common evolutionary descent—this only applies to one RNAP-associated transcription factor—Spt5, also known as NusG in bacteria. All other factors that aid RNAP during the transcription cycle are specific for the individual domain or only conserved between archaea and eukaryotes. Spt5 and its bacterial homologue NusG regulate gene expression in several ways by (i) modulating transcription processivity and promoter proximal pausing, (ii) coupling transcription and RNA processing or translation, and (iii) recruiting termination factors and thereby silencing laterally transferred DNA and protecting the genome against double-stranded DNA breaks. This review discusses recent discoveries that identify Spt5-like factors as evolutionary conserved nexus for the regulation and coordination of the machineries responsible for information processing in the cell.

Independent structural domains in paramyxovirus polymerase protein

All enzymatic activities required for genomic replication and transcription of nonsegmented negative strand RNA viruses (or Mononegavirales) are believed to be concentrated in the viral polymerase (L) protein. However, our insight into the organization of these different enzymatic activities into a bioactive tertiary structure remains rudimentary. Fragments of Mononegavirales polymerases analyzed to date cannot restore bioactivity through trans-complementation, unlike the related L proteins of segmented NSVs. We investigated the domain organization of phylogenetically diverse Paramyxovirus L proteins derived from measles virus (MeV), Nipah virus (NiV), and respiratory syncytial virus (RSV). Through a comprehensive in silico and experimental analysis of domain intersections, we defined MeV L position 615 as an interdomain candidate in addition to the previously reported residue 1708. Only position 1708 of MeV and the homologous positions in NiV and RSV L also tolerated the insertion of epitope tags. Splitting of MeV L at residue 1708 created fragments that were unable to physically interact and trans-complement, but strikingly, these activities were reconstituted by the addition of dimerization tags to the fragments. Equivalently split fragments of NiV, RSV, and MeV L oligomerized with comparable efficiency in all homo- and heterotypic combinations, but only the homotypic pairs were able to trans-complement. These results demonstrate that synthesis as a single polypeptide is not required for the Mononegavirales polymerases to adopt a proper tertiary conformation. Paramyxovirus polymerases are composed of at least two truly independent folding domains that lack a traditional interface but require molecular compatibility for bioactivity. The functional probing of the L domain architecture through trans-complementation is anticipated to be applicable to all Mononegavirales polymerases.

Bacteriophages LIMElight and LIMEzero of Pantoea agglomerans, belonging to the "phiKMV-like viruses"

Pantoea agglomerans is a common soil bacterium used in the biocontrol of fungi and bacteria but is also an opportunistic human pathogen. It has been described extensively in this context, but knowledge of bacteriophages infecting this species is limited. Bacteriophages LIMEzero and LIMElight of P. agglomerans are lytic phages, isolated from soil samples, belonging to the Podoviridae and are the first Pantoea phages of this family to be described. The double-stranded DNA (dsDNA) genomes (43,032 bp and 44,546 bp, respectively) encode 57 and 55 open reading frames (ORFs). Based on the presence of an RNA polymerase in their genomes and their overall genome architecture, these phages should be classified in the subfamily of the Autographivirinae, within the genus of the "phiKMV-like viruses." Phylogenetic analysis of all the sequenced members of the Autographivirinae supports the classification of phages LIMElight and LIMEzero as members of the "phiKMV-like viruses" and corroborates the subdivision into the different genera. These data expand the knowledge of Pantoea phages and illustrate the wide host diversity of phages within the "phiKMV-like viruses."

Activation of T7 RNA polymerase in Xenopus oocytes and cell-free extracts

Single-subunit bacteriophage T7 RNA polymerase (T7 RNAP) is universally employed for in vivo and in vitro transcription of genes put under control of the T7 promoter. The enzyme is capable of transcribing a complete gene without additional proteins. In this study, we reveal the presence of a low molecular weight factor, which induces several-fold activation of T7 RNAP in the cytoplasm of oocytes and eggs from Xenopus laevis. Cell-free reconstitution of the T7 RNAP activation allowed us to investigate the molecular properties of the activator, establish its peptide nature and suggest T7 RNAP activation mechanism. In contrast to the previously described nonspecific transcriptional activators, which interact with scattered ionic sites on nucleic acids, the peptide activator associates with T7 RNAP molecule, thus being a bona fide activator of the polymerase. To our knowledge, this is the first report concerning the specific activation of T7 RNAP by a factor of peptide or protein origin. Besides rather obvious merits in gaining more efficient transcription with T7 RNAP, this finding can provide additional insights into regulatory mechanisms of transcription. The study also introduces a novel highly sensitive luminescent assay of T7 RNAP activity.

Impaired function of the phage-type RNA polymerase RpoTp in transcription of chloroplast genes is compensated by a second phage-type RNA polymerase

Although chloroplast genomes are small, the transcriptional machinery is very complex in plastids of higher plants. Plastidial genes of higher plants are transcribed by plastid-encoded (PEP) and nuclear-encoded RNA polymerases (NEP). The nuclear genome of Arabidopsis contains two candidate genes for NEP, RpoTp and RpoTmp, both coding for phage-type RNA polymerases. We have analyzed the use of PEP and NEP promoters in transgenic Arabidopsis lines with altered RpoTp activities and in Arabidopsis RpoTp insertion mutants lacking functional RpoTp. Low or lacking RpoTp activity resulted in an albino phenotype of the seedlings, which normalized later in development. Differences in promoter usage between wild type and plants with altered RpoTp activity were also most obvious early in development. Nearly all NEP promoters were used in plants with low or lacking RpoTp activity, though certain promoters showed reduced or even increased usage. The strong NEP promoter of the essential ycf1 gene, however, was not used in mutant seedlings lacking RpoTp activity. Our data provide evidence for NEP being represented by two phage-type RNA polymerases (RpoTp and RpoTmp) that have overlapping as well as gene-specific functions in the transcription of plastidial genes.

Evidence for functional significance of the permuted C motif in Co2+-stimulated RNA-dependent RNA polymerase of infectious bursal disease virus

Segment B of bisegmented infectious bursal disease virus (IBDV) encodes virus protein 1 (VP1), possessing RNA-dependent RNA polymerase (RdRp) activity. This multidomain protein includes an RdRp domain with a non-canonical order of three sequence motifs forming the active site: C-A-B. The A-B-C order of the motifs, as found in RdRps of the majority of viruses, was converted by relocation (permutation) of motif C to a C-A-B order. Due to the unusual location and unproven significance, the motif was named 'C?'. This motif includes an Ala-Asp-Asn tripeptide that replaces the C motif Gly-Asp-Asp sequence, widely considered a hallmark of RdRps. In this study, functional significance of the C? motif was investigated by using purified His-tagged VP1 mutants with either a double replacement (ADN to GDD) or two single-site mutants (ADD or GDN). All mutants showed a significant reduction of RdRp activity in vitro, in comparison to that of VP1. Only the least-affected GDN mutant gave rise to viable, albeit partially impaired, progeny using a reverse-genetics system. Experiments performed to investigate whether the C motif was implicated in the control of metal dependence revealed that, compared with Mn2+ and Mg2+, Co2+ stimulated RdRp unconventionally. No activity was observed in the presence of several divalent cations. Of two Co2+ salts with Cl- and SO4(2-) anions, the former was a stronger stimulant for RdRp. When cell-culture medium was supplemented with 50 microM Co2+, an increase in IBDV progeny yield was observed. The obtained results provide evidence that the unusual Co2+ dependence of the IBDV RdRp might be linked to the permuted organization of the motif.

Faithful transcription initiation from a mitochondrial promoter in transgenic plastids

The transcriptional machineries of plastids and mitochondria in higher plants exhibit striking similarities. All mitochondrial genes and part of the plastid genes are transcribed by related phage-type RNA polymerases. Furthermore, the majority of mitochondrial promoters and a subset of plastid promoters show a similar structural organization. We show here that the plant mitochondrial atpA promoter is recognized by plastid RNA polymerases in vitro and in vivo. The Arabidopsis phage-type RNA polymerase RpoTp, an enzyme localized exclusively to plastids, was found to recognize the mitochondrial atpA promoter in in vitro assays suggesting the possibility that mitochondrial promoters might function as well in plastids. We have, therefore, generated transplastomic tobacco plants harboring in their chloroplast genome the atpA promoter fused to the coding region of the bacterial nptII gene. The chimeric nptII gene was found to be efficiently transcribed in chloroplasts. Mapping of the 5' ends of the nptII transcripts revealed accurate recognition of the atpA promoter by the chloroplast transcription machinery. We show further that the 5' untranslated region (UTR) of the mitochondrial atpA transcript is capable of mediating translation in chloroplasts. The functional and evolutionary implications of these findings as well as possible applications in chloroplast genome engineering are discussed.

DNA replication and transcription in mammalian mitochondria

The mitochondrion was originally a free-living prokaryotic organism, which explains the presence of a compact mammalian mitochondrial DNA (mtDNA) in contemporary mammalian cells. The genome encodes for key subunits of the electron transport chain and RNA components needed for mitochondrial translation. Nuclear genes encode the enzyme systems responsible for mtDNA replication and transcription. Several of the key components of these systems are related to proteins replicating and transcribing DNA in bacteriophages. This observation has led to the proposition that some genes required for DNA replication and transcription were acquired together from a phage early in the evolution of the eukaryotic cell, already at the time of the mitochondrial endosymbiosis. Recent years have seen a rapid development in our molecular understanding of these machineries, but many aspects still remain unknown.

Mitochondrial transcription and its regulation in mammalian cells

Human mitochondria contain multiple copies of a small double-stranded DNA genome that encode 13 components of the electron-transport chain and RNA components that are needed for mitochondrial translation. The mitochondrial genome is transcribed by a specialized machinery that includes a monomeric RNA polymerase, the mitochondrial transcription factor A and one of the two mitochondrial transcription factor B paralogues, TFB1M or TFB2M. Today, the components of the basal transcription machinery in mammalian mitochondria are known and their mechanisms of action are gradually being established. In addition, regulatory factors govern transcription levels both at the stage of initiation and termination, but the detailed biochemical understanding of these processes is largely missing.

Arabidopsis phage-type RNA polymerases: accurate in vitro transcription of organellar genes

The T7 bacteriophage RNA polymerase (RNAP) performs all steps of transcription, including promoter recognition, initiation, and elongation as a single-polypeptide enzyme. Arabidopsis thaliana possesses three nuclear-encoded T7 phage-type RNAPs that localize to mitochondria (RpoTm), plastids (RpoTp), or presumably both organelles (RpoTmp). Their specific functions are as yet unresolved. We have established an in vitro transcription system to examine the abilities of the three Arabidopsis phage-type RNAPs to synthesize RNA and to recognize organellar promoters. All three RpoT genes were shown to encode transcriptionally active RNAPs. RpoTmp displayed no significant promoter specificity, whereas RpoTm and RpoTp were able to accurately initiate transcription from overlapping subsets of mitochondrial and plastidial promoters without the aid of protein cofactors. Our study strongly suggests RpoTm to be the enzyme that transcribes most, if not all, mitochondrial genes in Arabidopsis. Intrinsic promoter specificity, a feature that RpoTm and RpoTp share with the T7 RNAP, appears to have been conserved over the long period of evolution of nuclear-encoded mitochondrial and plastidial RNAPs. Selective promoter recognition by the Arabidopsis phage-type RNAPs in vitro implies that auxiliary factors are required for efficient initiation of transcription in vivo.