The reverse-transcription polyermase chain reaction (PCR) assay works as follows: within target cells, genomic DNA (top) is naturally transcribed into messenger RNA (mRNA); this can be subsequently isolated using a variety of techniques. mRNA is then converted into complementary DNA (cDNA) by an RNA- dependent DNA polymerase, termed reverse transcriptase. Next, the cDNA is changed into double-stranded DNA, becoming the template for a subsequent PCR reaction. After the amplification reaction, the product can be visualized by gel electrophoresis (bottom).
