Reverse Transcriptase

When reverse transcriptase was first described, it was believed to be a peculiarity of retroviruses. However, researchers now know that reverse transcription also occurs during the replication of the DNA virus hepatitis B, and that RNA-copying DNA polymerases function within human cells. One of these host reverse transcriptases is telomerase, an enzyme that helps maintain chromosome ends.

Other human reverse transcriptases are parts of endogenous retroviruses and retroelements, such as those that encoded the majority of the repetitive "junk" DNA in human chromosomes. Many of these retroelements integrated their DNAs into our chromosomes so long ago that they predate human speciation. Because of this, molecular phylogeneticists can use sites of retroelement insertions to determine the lineages and ancestral relationships of species. Thus, while retroviruses, in the form of HIV-1, represent one of the newest diseases of humans, the prevalence of other retrovirus-like elements in our genomes demonstrates the long-standing relationship of humans with reverse transcribing elements.