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Reverse transcriptase (RT) inhibition of PCR at low concentrations of template and its implications for quantitative RT-PCR.

ABSTRACT: Numerous instances of reverse transcriptase (RT) inhibition of the PCR were observed while developing nonquantitative uncoupled RT-PCR techniques for detecting nitrogenase and ammonia monooxygenase gene expression in situ. The inhibitory effect of RT on the PCR was removed with increasing template concentrations beyond 10(5) to 10(6) copies. Including T4 gene 32 protein during the reverse transcription phase of the RT-PCR reaction increased the RT-PCR product yield by as much as 483%; if gene 32 protein was introduced after reverse transcription but prior to the PCR phase, no improvement in product yield was observed. Addition of 1 microgram of exogenous calf thymus DNA or yeast tRNA did little to relieve RT inhibition of the PCR on both genomic DNA and mRNA templates. These results suggest that RT inhibition of the PCR is mediated through direct interaction with the specific primer-template combination (DNA and RNA) and point to specific assay modifications for estimating the extent of RT inhibition and counteracting some of the inhibitory effect. Furthermore, the working hypothesis of RT inhibition below a 10(5) to 10(6) copy threshold has important implications for quantitative RT-PCR studies. In particular, competitive, quantitative RT-PCR systems will consistently underestimate the actual RNA concentration. Hence, enumerations of RNA templates below 10(5) to 10(6) copies will be relative to an internal standard and will not be an absolute measure of RNA abundance in situ.

SUBMITTER: Chandler DP

PROVIDER: S-EPMC106100 | biostudies-literature | 1998 Feb

REPOSITORIES: biostudies-literature

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Reverse transcriptase (RT) inhibition of PCR at low concentrations of template and its implications for quantitative RT-PCR.

Chandler D P DP Wagnon C A CA Bolton H H

Applied and environmental microbiology 19980201 2

Numerous instances of reverse transcriptase (RT) inhibition of the PCR were observed while developing nonquantitative uncoupled RT-PCR techniques for detecting nitrogenase and ammonia monooxygenase gene expression in situ. The inhibitory effect of RT on the PCR was removed with increasing template concentrations beyond 10(5) to 10(6) copies. Including T4 gene 32 protein during the reverse transcription phase of the RT-PCR reaction increased the RT-PCR product yield by as much as 483%; if gene 32 ...[more]

PMID: 9464406

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Project description:BackgroundIn functional genomics, transcript measurement is of fundamental importance. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays are the most popular technology and depend on the initial molecular step, the reverse transcription (RT). This study provides a complex overview of the influence of elements such as RT systems, amount of background RNA, and transcript abundance on the efficiency of qRT-PCR. Using qRT-PCR, we compared the efficiency of some commonly used RT systems and measured the production of PCR-amplifiable products and the influence of PCR inhibitor contents.ResultsThe qRT-PCR assays were conducted using the TaqMan system, although we also tested the SYBR Green I chemistry, which is not compatible with all the RT systems. When dealing with low-abundance transcripts, the SuperScript II system generated more detectable molecules than the four other systems tested: Sensiscript, Omniscript, SuperScript III and PowerScript (P < 0.05). However, the Sensiscript and PowerScript systems were more efficient for detecting high-abundance transcripts in the presence of 1 to 2 mug background RNA (P < 0.05). The most striking aspect was the influence of the dilution of the RT reaction on the subsequent PCR. Indeed, some inhibition was released when diluted RT reactions were used for the quantitative PCR measurements. Furthermore, the amount of background RNA in the RT reaction was also a major component influencing a downstream step in qRT-PCR, the PCR reaction. Whereas Sensiscript was less biased, the other systems contained an important source of PCR inhibitors, interfering as much as 70% with the qRT-PCR.ConclusionThis study provides a complex overview of the influence of elements such as RT systems, qRTPCR chemistry, amount of background RNA, and transcript abundance on the efficiency of qRT-PCR. Whereas the most significant influencing factor is the presence of inhibitors in the RT systems, total background RNA is also a major influencing component that affects the PCR reaction. Whenever the aim of a study is to obtain a precise gene expression measurement or to profile the global transcriptome (e.g. microarray), the RT step is critical and should be examined with care.

Project description:Most individuals acutely infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exhibit mild symptoms. However, 10 to 20% of those infected develop long-term symptoms, referred to as post-coronavirus disease 2019 (COVID-19) condition (PCC). One hypothesis is that PCC might be exacerbated by viral persistence in tissue sanctuaries. Therefore, the accurate detection and quantification of SARS-CoV-2 are not only necessary for viral load monitoring but also crucial for detecting long-term viral persistence and determining whether viral replication is occurring in tissue reservoirs. In this study, the sensitivity and robustness of reverse transcription (RT)-droplet digital PCR (ddPCR) and RT-quantitative PCR (qPCR) techniques have been compared for the detection and quantification of SARS-CoV-2 genomic and subgenomic RNAs from oropharyngeal swabs taken from confirmed SARS-CoV-2-positive, SARS-CoV-2-exposed, and nonexposed individuals as well as from samples from mice infected with SARS-CoV-2. Our data demonstrated that both techniques presented equivalent results in the mid- and high-viral-load ranges. Additionally, RT-ddPCR was more sensitive than RT-qPCR in the low-viral-load range, allowing the accurate detection of positive results in individuals exposed to the virus. Overall, these data suggest that RT-ddPCR might be an alternative to RT-qPCR for detecting low viral loads in samples and for assessing viral persistence in samples from individuals with PCC. IMPORTANCE We developed one-step reverse transcription (RT)-droplet digital PCR (ddPCR) protocols to detect SARS-CoV-2 RNA and compared them to the gold-standard RT-quantitative PCR (RT-qPCR) method. RT-ddPCR was more sensitive than RT-qPCR in the low-viral-load range, while both techniques were equivalent in the mid- and high-viral-load ranges. Overall, these results suggest that RT-ddPCR might be a viable alternative to RT-qPCR when it comes to detecting low viral loads in samples, which is a highly relevant issue for determining viral persistence in as-yet-unknown tissue reservoirs in individuals suffering from post-COVID conditions or long COVID.

Project description:Emerging SARS-CoV-2 (SC-2) variants with increased infectivity and vaccine resistance are of major concern. Rapid identification of such variants is important for the public health decision making and to provide valuable data for epidemiological and policy decision making. We developed a multiplex reverse transcriptase quantitative PCR (RT-qPCR) assay that can specifically identify and differentiate between the emerging B.1.1.7 and B.1.351 SC-2 variants. In a single assay, we combined four reactions-one that detects SC-2 RNA independently of the strain, one that detects the D3L mutation, which is specific to variant B.1.1.7, one that detects the 242 to 244 deletion, which is specific to variant B.1.351, and the fourth reaction, which identifies the human RNAseP gene, serving as an endogenous control for RNA extraction integrity. We show that the strain-specific reactions target mutations that are strongly associated with the target variants and not with other major known variants. The assay's specificity was tested against a panel of respiratory pathogens (n = 16), showing high specificity toward SC-2 RNA. The assay's sensitivity was assessed using both in vitro transcribed RNA and clinical samples and was determined to be between 20 and 40 viral RNA copies per reaction. The assay performance was corroborated with Sanger and whole-genome sequencing, showing complete agreement with the sequencing results. The new assay is currently implemented in the routine diagnostic work at the Central Virology Laboratory, and may be used in other laboratories to facilitate the diagnosis of these major worldwide-circulating SC-2 variants. IMPORTANCE This study describes the design and utilization of a multiplex reverse transcriptase quantitative PCR (RT-qPCR) to identify SARS-COV-2 (SC2) RNA in general and, specifically, to detect whether it is of lineage B.1.1.7 or B.1.351. Implementation of this method in diagnostic and research laboratories worldwide may help the efforts to contain the COVID-19 pandemic. The method can be easily scaled up and be used in high-throughput laboratories, as well as small ones. In addition to immediate help in diagnostic efforts, this method may also help in epidemiological studies focused on the spread of emerging SC-2 lineages.

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Reverse transcriptase (RT) inhibition of PCR at low concentrations of template and its implications for quantitative RT-PCR.

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Reverse transcriptase (RT) inhibition of PCR at low concentrations of template and its implications for quantitative RT-PCR.

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