Reverse Transcriptase

Reverse transcriptase went on to play a critical role in the molecular revolution of the late 1970s and 1980s, especially in the fields of gene discovery and biotechnology. Genes can often be discovered most easily by isolating and analyzing the messenger RNA (mRNA) production in a cell. Reverse transcriptase allowed the synthesis of cDNA, or complementary copies of messenger RNAs. The cDNA can then be expressed in a model organism such as Escherichia coli, and the protein it codes for can then be made in abundance. The cloning of cDNA was instrumental to gene discovery in the later part of the twentieth century. Using cDNA copies of genes is necessary when bacteria are used to produce human protein-based pharmaceuticals. This is because bacteria lack the machinery necessary to recognize unspliced genes, but bacteria can use cDNAs to direct the synthesis of human or other higher organism proteins.

Even though the human genome sequence was reported in 2001, copying RNAs with reverse transcriptase remains important. One reason for this is that some human diseases result from mutations in genes whose products act to adjust the sequences of RNAs after transcription but before protein synthesis. Thus, even though prototype human sequences are available, it appears likely that molecular diagnostics will include screening cDNA copies of individual people's RNAs. Other uses of cDNA include generating probes to screen microarrays to assess variation in gene expression and regulation.