The short lengths of microRNAs (miRNAs) present a significant challenge for detection and quantitation using conventional methods for RNA analysis. To address this problem, we developed a quantitative, sensitive, and rapid miRNA assay based on our previously described messenger RNA Invader assay. This assay was used successfully in the analysis of several miRNAs, using as little as 50-100 ng of total cellular RNA or as few as 1,000 lysed cells. Its specificity allowed for discrimination between miRNAs differing by a single nucleotide, and between precursor and mature miRNAs. The Invader miRNA assay, which can be performed in unfractionated detergent lysates, uses fluorescence detection in microtiter plates and requires only 2-3 h incubation time, allowing for parallel analysis of multiple samples in high-throughput screening analyses.
RNA quantitation is becoming increasingly important in basic, pharmaceutical, and clinical research. For example, quantitation of viral RNAs can predict disease progression and therapeutic efficacy. Likewise, gene expression analysis of diseased versus normal, or untreated versus treated, tissue can identify relevant biological responses or assess the effects of pharmacological agents. As the focus of the Human Genome Project moves toward gene expression analysis, the field will require a flexible RNA analysis technology that can quantitatively monitor multiple forms of alternatively transcribed and/or processed RNAs (refs 3,4). We have applied the principles of invasive cleavage and engineered an improved 5'-nuclease to develop an isothermal, fluorescence resonance energy transfer (FRET)-based signal amplification method for detecting RNA in both total RNA and cell lysate samples. This detection format, termed the RNA invasive cleavage assay, obviates the need for target amplification or additional enzymatic signal enhancement. In this report, we describe the assay and present data demonstrating its capabilities for sensitive (<100 copies per reaction), specific (discrimination of 95% homologous sequences, 1 in > or =20,000), and quantitative (1.2-fold changes in RNA levels) detection of unamplified RNA in both single- and biplex-reaction formats.
The removal of impurities and contaminants from PCR‐amplified fragments is important for mutation detection methods which identify mutations based on shifts in electrophoretic mobility. This is particularly critical for assays and detection methods which use target DNA that is labeled prior to analysis and electrophoretic detection. We examined several procedures for purifying DNA amplified by the polymerase chain reaction (PCR) and their use in conjunction with a novel DNA scanning method, the Cleavase fragment length polymorphism (CFLP)* assay. In this study, a 480 bp DNA fragment, fluorescently labeled on the 5′‐end of one strand, was amplified and subjected to various widely used purification procedures, including several commercially available clean‐up kits. We demonstrate that visualization of the fluorescent label, as opposed to simple ethidium bromide staining, reveals the presence of considerable levels of labeled, truncated, amplification products. The various procedures were evaluated on the basis of their ability to remove these unwanted DNA fragments as well as on the degree to which they inhibited or promoted the CFLP reaction. Several procedures are recommended for use with CFLP analysis, including isopropanol precipitation, gel excision, and several commercially available spin columns. Concurrently, we evaluated (compared) a number of commonly used visualization platforms, including fluorescence imaging, chemiluminescence, and post‐electrophoretic staining, for the ability to detect CFLP pattern changes. The advantages and disadvantages of different methods are discussed and amounts of DNA to be used for CFLP analysis on different detection platforms are recommended.
Institute which is the training organization for the John Zink Co. LLC in Tulsa, OK which is a leading manufacturer of industrial combustion equipment. Dr. Baukal has over 30 years of industrial experience and over 20 years of teaching experience. He is a licensed Professional Engineer, has authored or edited 8 books on industrial combustion, and is an inventor on 11 U.S. patents.
The Invader assay is a homogeneous, isothermal, signal amplification system for the quantitative detection of nucleic acids. The assay can directly detect either DNA or RNA without target amplification or reverse transcription. It is based on the ability of Cleavase enzymes to recognize as a substrate and cleave a specific nucleic acid structure generated through the hybridization of two oligonucleotides to the target sequence. The combination of sequence-specific oligonucleotide hybridization and structure-specific enzymatic cleavage results in a highly specific assay well suited for discriminating closely related gene sequences. This includes detection of single nucleotide polymorphisms directly from genomic DNA as well as highly homologous mRNAs in closely related gene families. Because Cleavase substrate recognition is structure, and not sequence dependent, cleavage and detection can be applied to virtually any DNA or RNA sequence.
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