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Appl Environ Microbiol, February 1998, p. 669-677, Vol. 64, No. 2
Pacific Northwest National Laboratory,
Environmental Microbiology, Richland, Washington 99352
Received 25 March 1997/Accepted 22 November 1997
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 105 to
106 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 µg 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 105 to
106 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
105 to 106 copies will be relative to an
internal standard and will not be an absolute measure of RNA abundance
in situ.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Reverse Transcriptase (RT) Inhibition of PCR at Low
Concentrations of Template and Its Implications for Quantitative
RT-PCR
*
Corresponding author. Mailing address: Pacific
Northwest National Laboratory, Environmental Microbiology, 900 Battelle
Blvd., Mail Stop K4-06, Richland, WA 99352. Phone: (509) 375-2543. Fax: (509) 375-6666. E-mail: dp_chandler{at}pnl.gov.
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