Simultaneous amplification and screening of whole plasmids using the T7 bacteriophage replisome

Chimeric DNA byproducts in strand displacement amplification using the T7 replisome

Recent advances in next generation sequencing technologies enable reading DNA molecules hundreds of kilobases in length and motivate development of DNA amplification methods capable of producing long amplicons. In vivo, DNA replication is performed not by a single polymerase enzyme, but multiprotein complexes called replisomes. Here, we investigate strand-displacement amplification reactions using the T7 replisome, a macromolecular complex of a helicase, a single-stranded DNA binding protein, and a DNA polymerase. The T7 replisome may initiate processive DNA synthesis from DNA nicks, and the reaction of a 48 kilobase linear double stranded DNA substrate with the T7 replisome and nicking endonucleases is shown to produce discrete DNA amplicons. To gain a mechanistic understanding of this reaction, we utilized Oxford Nanopore long-read sequencing technology. Sequence analysis of the amplicons revealed chimeric DNA reads and uncovered a connection between template switching and polymerase exonuclease activity. Nanopore sequencing provides insight to guide the further development of isothermal amplification methods for long DNA, and our results highlight the need for high-specificity, high-turnover nicking endonucleases to initiate DNA amplification without thermal denaturation.

A novel isothermal method for amplification of long specific amplicon from linear template

Isothermal nucleic acid amplification methods have been successfully developed and applied for diagnostic purpose, especially for detection of pathogens. However, amplicon size of such methods is relatively short (< 500 bp) to limit their application for long amplicon production that can be used for various downstream applications including genomic surveillance of pathogens. To fill the gap, we developed a method for specific amplification of kilobases-long target sequence from RNA templates. This method, named CREA, utilizes sequence specific recombination of Cre recombinase to generate circular intermediate template for subsequent RCA reaction. CREA with SARS-CoV-2 spike template could amplify ~ 2.9 kb target and up to ~ 1.9 kb amplicon was able to produce in sufficient amount for general cloning. Each step of CREA procedure was thoroughly analyzed to provide directions for further optimizations. Furthermore, we evaluated a variation of CREA which utilized DNA ligase.

Reconstitution and Coupling of DNA Replication and Segregation in a Biomimetic System

A biomimetic system capable of replication and segregation of genetic material constitutes an essential component for the future design of a minimal synthetic cell. Here we have used the simple T7 bacteriophage system and the plasmid-derived ParMRC system to establish in vitro DNA replication and DNA segregation, respectively. These processes were incorporated into biomimetic compartments providing an enclosed reaction space. The functional lifetime of the encapsulated segregation system could be prolonged by equipping it with ATP-regenerating and oxygen-scavenging systems. Finally, we showed that DNA replication and segregation processes could be coupled in vitro by using condensed DNA nanoparticles resulting from DNA replication. ParM spindles extended over tens of micrometers and could thus be used for segregation in compartments that are significantly longer than bacterial cell size. Overall, this work demonstrates the successful bottom-up assembly and coupling of molecular machines that mediate replication and segregation, thus providing an important step towards the development of a fully functional minimal cell.

An efficient isothermal PCR method for on-site detection of nucleic acid

Convective PCR (CPCR) is an isothermal nucleic acid amplification technology; however, natural convection exhibits a chaotic and multiplex flow state, resulting in low amplification efficiency and specificity. We placed a polycarbonate strip (p-strip) inside reaction tubes to induce circumfluence by blocking the inner ring that originally allowed fluid to flow at suboptimal temperatures. Moreover, we constructed a dual-temperature instrument to provide appropriate denaturing and annealing zones for CPCR. Tubes containing p-strips exhibited significantly improved efficiency, sensitivity and specificity. For real-time detection, the variation coefficients of three replicates having the same concentrations were less than 2% in more than half of the cases, indicating improved CPCR amplification and potential as a commercial on-site nucleic acid diagnosis tool.

Aligner-mediated cleavage of nucleic acids and its application to isothermal exponential amplification

A programmable sequence-specific aligner-mediated cleavage endows strand displacement amplification with excellent universality, high sensitivity, high specificity and simple primer design.

We herein describe a simple and versatile approach to use conventional nicking endonuclease (NEase) for programmable sequence-specific cleavage of DNA, termed aligner-mediated cleavage (AMC), and its application to DNA isothermal exponential amplification (AMC-based strand displacement amplification, AMC-SDA). AMC uses a hairpin-shaped DNA aligner (DA) that contains a recognition site in its stem and two side arms complementary to target DNA. Thus, it enables the loading of an NEase on DA's stem, localization to a specific locus through hybridization of the side arms with target DNA, and cleavage thereof. By using just one NEase, it is easy to make a break at any specific locus and tune the cleavage site to the single-nucleotide scale. This capability also endows the proposed AMC-SDA with excellent universality, since the cleavage of target DNA, followed by a polymerase-catalyzed extension along a particular primer as a key step for initiating SDA, no longer relies on any special sequence. Moreover, this manner of initiation facilitates the adoption of 3′-terminated primers, thus making AMC-SDA highly sensitive and highly specific, as well as simple primer design.

PCR Technologies for Point of Care Testing: Progress and Perspectives

Since the Human Genome Project completed in 2000, the sequencing of the first genome, massive progress has been made by medical science in the early diagnosis and personalized therapies based on nucleic acids (NA) analysis. To allow the extensive use of these molecular methods in medical practice, scientific research is nowadays strongly focusing on the development of new miniaturized and easy-to-use technologies and devices allowing fast and low cost NA analysis in decentralized environments. It is now the era of so-called genetic "Point-of-Care" (PoC). These systems must integrate and automate all steps necessary for molecular analysis such as sample preparation (extraction and purification of NA) and detection based on PCR (Polymerase Chain Reaction) technology in order to perform, by unskilled personnel, in vitro genetic analysis near the patient (in hospital, in the physician office, clinic, or home), with rapid answers and low cost. In this review, the recent advances in genetic PoC technologies are discussed, including the extraction and PCR amplification chemistry suitable for PoC use and the new frontiers of research in this field.

A one-step dipstick assay for the on-site detection of nucleic acid

OBJECTIVES

We have developed a one-step nucleic acid dipstick assay (NADA) for visually detecting polymerase chain reaction (PCR) products within 3min. "One-step" means that there were no additional procedures between amplification and detection.

METHODS

This method was achieved through the use of asymmetric PCR and specially designed probes with appropriate melting temperature values. We initially combined one-step NADA with asymmetric capillary convective PCR (ACCPCR), an easy and rapid nucleic acid amplification technique, to construct an on-site nucleic acid diagnostic platform.

RESULTS

We developed a diagnostic assay for the hepatitis B virus based on the ACCPCR-NADA platform to verify its feasibility. It exhibited an analytical sensitivity of three copies per test and a broad detection spectrum including genotype A-I. It also showed 97.9% sensitivity and 100% specificity based on the results observed using 67 serum samples with the Roche COBAS AmpliPrep/COBAS TaqMan (COBAS) system as the standard for comparison.

CONCLUSION

The results provide evidence for the feasibility of using an ACCPCR-NADA platform in practical applications, especially in on-site test.

Sample pretreatment and nucleic acid-based detection for fast diagnosis utilizing microfluidic systems

Recently, micro-electro-mechanical-systems (MEMS) technology and micromachining techniques have enabled miniaturization of biomedical devices and systems. Not only do these techniques facilitate the development of miniaturized instrumentation for biomedical analysis, but they also open a new era for integration of microdevices for performing accurate and sensitive diagnostic assays. A so-called “micro-total-analysis-system”, which integrates sample pretreatment, transport, reaction, and detection on a small chip in an automatic format, can be realized by combining functional microfluidic components manufactured by specific MEMS technologies. Among the promising applications using microfluidic technologies, nucleic acid-based detection has shown considerable potential recently. For instance, micro-polymerase chain reaction chips for rapid DNA amplification have attracted considerable interest. In addition, microfluidic devices for rapid sample pretreatment prior to nucleic acid-based detection have also achieved significant progress in the recent years. In this review paper, microfluidic systems for sample preparation, nucleic acid amplification and detection for fast diagnosis will be reviewed. These microfluidic devices and systems have several advantages over their large-scale counterparts, including lower sample/reagent consumption, lower power consumption, compact size, faster analysis, and lower per unit cost. The development of these microfluidic devices and systems may provide a revolutionary platform technology for fast sample pretreatment and accurate, sensitive diagnosis.

Isothermal DNA amplification using the T4 replisome: circular nicking endonuclease-dependent amplification and primase-based whole-genome amplification

In vitro reconstitution of the bacteriophage T4 replication machinery provides a novel system for fast and processive isothermal DNA amplification. We have characterized this system in two formats: (i) in circular nicking endonuclease-dependent amplification (cNDA), the T4 replisome is supplemented with a nicking endonuclease (Nb.BbvCI) and a reverse primer to generate a well-defined uniform double-stranded linear product and to achieve up to 1100-fold linear amplification of a plasmid in 1 h. (ii) The T4 replisome with its primase (gp61) can also support priming and exponential amplification of genomic DNA in primase-based whole-genome amplification (T4 pWGA). Low amplification biases between 4.8 and 9.8 among eight loci for 0.3–10 ng template DNA suggest that this method is indeed suitable for uniform whole-genome amplification. Finally, the utility of the T4 replisome for isothermal DNA amplification is demonstrated in various applications, including incorporation of functional tags for DNA labeling and immobilization; template generation for in vitro transcription/translation and sequencing; and colony screening and DNA quantification.

Isothermal DNA amplification in vitro: the helicase-dependent amplification system

Since the development of polymerase chain reaction, amplification of nucleic acids has emerged as an elemental tool for molecular biology, genomics, and biotechnology. Amplification methods often use temperature cycling to exponentially amplify nucleic acids; however, isothermal amplification methods have also been developed, which do not require heating the double-stranded nucleic acid to dissociate the synthesized products from templates. Among the several methods used for isothermal DNA amplification, the helicase-dependent amplification (HDA) is discussed in this review with an emphasis on the reconstituted DNA replication system. Since DNA helicase can unwind the double-stranded DNA without the need for heating, the HDA system provides a very useful tool to amplify DNA in vitro under isothermal conditions with a simplified reaction scheme. This review describes components and detailed aspects of current HDA systems using Escherichia coli UvrD helicase and T7 bacteriophage gp4 helicase with consideration of the processivity and efficiency of DNA amplification.

Nucleic acid isothermal amplification technologies: a review

Nucleic acid amplification technologies are used in the field of molecular biology and recombinant DNA technologies. These techniques are used as leading methods in detecting and analyzing a small quantity of nucleic acids. The polymerase chain reaction (PCR) is the most widely used method for DNA amplification for detection and identification of infectious diseases, genetic disorders and other research purposes. However, it requires a thermocycling machine to separate two DNA strands and then amplify the required fragment. Novel developments in molecular biology of DNA synthesis in vivo demonstrate the possibility of amplifying DNA in isothermal conditions without the need of a thermocycling apparatus. DNA polymerase replicates DNA with the aid of various accessory proteins. Recent identification of these proteins has enabled development of new in vitro isothermal DNA amplification methods, mimicking these in vivo mechanisms. There are several types of isothermal nucleic acid amplification methods such as transcription mediated amplification, nucleic acid sequence-based amplification, signal mediated amplification of RNA technology, strand displacement amplification, rolling circle amplification, loop-mediated isothermal amplification of DNA, isothermal multiple displacement amplification, helicase-dependent amplification, single primer isothermal amplification, and circular helicase-dependent amplification. In this article, we review these isothermal nucleic acid amplification technologies and their applications in molecular biological studies.