The central dogma of molecular biology states that DNA is transcribed into RNA which is then translated into proteins. The discovery of viruses that have an RNA genome is one example that shows there are exceptions to this universal notion. Upon infection of a host cell, the RNA genome of a retrovirus is converted into DNA, by a process called reverse transcription which uses a virus-encoded reverse transcriptase enzyme, and then integrated into the genome of the host. Investigations focusing on reverse transcription, have lead to the discovery of common sequence elements called retrotransposons that also utilize reverse transcription to make DNA elements that are inserted into genomes. These elements are common in eukaryotes and it is estimated that at least 40% of human genomic DNA consists of retrotransposons.
- Cooper, Geoffery M. The Cell: A Molecular Approach. 4th ed. Washington D.C.: ASM
Press, 2007. 115-117.