Molecular Biology


Protocols in Current Issue
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0 Q&A 2049 Views Nov 5, 2021

The ongoing COVID-19 pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). As this virus is classified as a biosafety level-3 (BSL-3) agent, the development of countermeasures and basic research methods is logistically difficult. Recently, using reverse genetics, we developed a BSL-2 cell culture system for production of transcription- and replication-component virus-like-particles (trVLPs) by genetic transcomplementation. The system consists of two parts: SARS-CoV-2 GFP/ΔN genomic RNA, in which the nucleocapsid (N) gene, a critical gene for virion packaging, is replaced by a GFP reporter gene; and a packaging cell line for ectopic expression of N (Caco-2-N). The complete viral life cycle can be recapitulated and confined to Caco-2-N cells, with GFP positivity serving as a surrogate readout for viral infection. In addition, we utilized an intein-mediated protein splicing technique to split the N gene into two independent vectors and generated the Caco-2-Nintein cells as a packaging cell line to further enhance the security of this cell culture model. Altogether, this system provides for a safe and convenient method to produce trVLPs in BSL-2 laboratories. These trVLPs can be modified to incorporate desired mutations, permitting high-throughput screening of antiviral compounds and evaluation of neutralizing antibodies. This protocol describes the details of the trVLP cell culture model to make SARS-CoV-2 research more readily accessible.

0 Q&A 4844 Views Oct 20, 2020
CRISPR/Cas9 system directed by a gene-specific single guide RNA (sgRNA) is an effective tool for genome editing such as deletions of few bases in coding genes. However, targeted deletion of larger regions generate loss-of-function alleles that offer a straightforward starting point for functional dissections of genomic loci. We present an easy-to-use strategy including a fast cloning dual-sgRNA vector linked to efficient isolation of heritable Cas9-free genomic deletions to rapidly and cost-effectively generate a targeted heritable genome deletion. This step-by-step protocol includes gRNA design, cloning strategy and mutation detection for Arabidopsis and may be adapted for other plant species.
0 Q&A 5219 Views Jun 5, 2019
The construction of Hybrid minigenes provides a robust and simple strategy to study the effects of disease-causing mutations on mRNA splicing when biological material from patient cells is not available. Hybrid minigenes can be used as splicing reporter plasmids allow RNA expression and heterologous splicing reactions between synthetic splicing signals in the vector and endogenous splicing signals in a cloned genomic DNA fragment that contains one or more introns and exons. Minigene-based assay has been used extensively to test the effect of mutations in the splicing of a target sequence. They can also be used to test the ability of CRISPR/Cas9 and one or more associated gRNAs to target specific sequences in the minigene, and determine the effect of these editing events on splicing. As an example, it is shown that CRISPR/Cas9-based, targeted excision of short intronic sequences containing mutations which create cryptic splice signals, can restore normal splicing in a CFTR Hybrid minigene.
0 Q&A 6575 Views Oct 5, 2018
Corynebacterium glutamicum is a versatile workhorse for industrial bioproduction of many kinds of chemicals and fuels, notably amino acids. Development of advanced genetic engineering tools is urgently demanded for systems metabolic engineering of C. glutamicum. Recently unveiled clustered regularly interspaced short palindromic repeats (CRISPR) and their CRISPR-associated proteins (Cas) are now revolutionizing genome editing. The CRISPR/Cas9 system from Streptococcus pyogenes that utilizes NGG as protospacer adjacent motif (PAM) and has good targeting specificity can be developed into a powerful tool for efficient and precise genome editing of C. glutamicum. In this protocol, we described the general procedure for CRISPR/Cas9-mediated ssDNA recombineering in C. glutamicum. Small modifications can be introduced into the C. glutamicum chromosome with a high editing efficiency up to 90%.
0 Q&A 10752 Views Apr 20, 2018
Candida albicans is the most prevalent and important human fungal pathogen. The advent of CRISPR as a means of gene editing has greatly facilitated genetic analysis in C. albicans. Here, we describe a detailed step-by-step procedure to construct and analyze C. albicans deletion mutants. This protocol uses plasmids that allow simple ligation of synthetic duplex 23mer guide oligodeoxynucleotides for high copy gRNA expression in C. albicans strains that express codon-optimized Cas9. This protocol allows isolation and characterization of deletion strains within nine days.
1 Q&A 17305 Views Mar 20, 2018
Genome modification in budding yeast has been extremely successful largely due to its highly efficient homology-directed DNA repair machinery. Several methods for modifying the yeast genome have previously been described, many of them involving at least two-steps: insertion of a selectable marker and substitution of that marker for the intended modification. Here, we describe a CRISPR-Cas9 mediated genome editing protocol for modifying any yeast gene of interest (either essential or nonessential) in a single-step transformation without any selectable marker. In this system, the Cas9 nuclease creates a double-stranded break at the locus of choice, which is typically lethal in yeast cells regardless of the essentiality of the targeted locus due to inefficient non-homologous end-joining repair. This lethality results in efficient repair via homologous recombination using a repair template derived from PCR. In cases involving essential genes, the necessity of editing the genomic lesion with a functional allele serves as an additional layer of selection. As a motivating example, we describe the use of this strategy in the replacement of HEM2, an essential yeast gene, with its corresponding human ortholog ALAD.
0 Q&A 7176 Views Nov 20, 2017
The advent of single cell genomics and the continued use of metagenomic profiling in diverse environments has exponentially increased the known diversity of life. The recovered and assembled genomes predict physiology, consortium interactions and gene function, but experimental validation of metabolisms and molecular pathways requires more directed approaches. Gene function–and the correlation between phenotype and genotype is most obviously studied with genetics, and it is therefore critical to develop techniques permitting rapid and facile strain construction. Many new and candidate archaeal lineages have recently been discovered, but experimental, genetic access to archaeal genomes is currently limited to a few model organisms. The results obtained from manipulating the genomes of these genetically-accessible organisms have already had profound effects on our understanding of archaeal physiology and information processing systems, and these continued studies also help resolve phylogenetic reconstruction of the tree of life. The hyperthermophilic, planktonic, marine heterotrophic archaeon Thermococcus kodakarensis, has emerged as an ideal genetic system with a suite of techniques available to add or delete encoded activities, or modify expression of genes in vivo. We outline here techniques to rapidly and markerlessly delete a single, or repetitively delete several, continuous sequences from the T. kodakarensis genome. Our procedure includes details on the construction of the plasmid DNA necessary for transformation that directs, via homologous recombination, integration into the genome, identification of strains that have incorporated plasmid sequences (termed intermediate strains), and confirmation of plasmid excision, leading to deletion of the target gene in final strains. Near identical procedures can be employed to modify, rather than delete, a genomic locus.
0 Q&A 10944 Views Sep 20, 2017
Genome manipulation has become more accessible given the advent of the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) editing technology. The Cas9 endonuclease binds a single stranded (single guide) RNA (sgRNA) fragment that recruits the complex to a corresponding genomic target sequence where it induces a double stranded break. Eukaryotic repair systems allow for the introduction of exogenous DNA, repair of existing mutations, or deletion of endogenous gene products. Targeting of Cas9 to multiple genomic positions (termed ‘multiplexing’) is achieved by the expression of multiple sgRNAs within the same nucleus. However, an ongoing concern of the CRISPR field has been the accidental targeting of Cas9 to alternative (‘off-target’) DNA locations within a genome. We describe the use (dubbed Multiplexing of Cas9 at Artificial Loci) of installed artificial Cas9 target sequences into the yeast genome that allow for (i) multiplexing with a single sgRNA; (ii) a reduction/elimination in possible off-target effects, and (iii) precise control of the placement of the intended target sequence(s).
0 Q&A 9638 Views May 20, 2017
Chromosome engineering is an important technology with applications in basic biology and biotechnology. Chromosome splitting technology called PCS (PCR-mediated Chromosome Splitting) has already been developed as a fundamental chromosome engineering technology in the budding yeast. However, the splitting efficiency of PCS technology is not high enough to achieve multiple splitting at a time. This protocol describes a procedure for achieving simultaneous and multiple chromosome splits in the budding yeast Saccharomyces cerevisiae by a new technology called CRISPR-PCS. At least four independent sites in the genome can be split by one transformation. Total time and labor for obtaining a multiple split yeast strain is drastically reduced when compared with conventional PCS technology.

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