Elizabeth Blackburn and the Story of Telomeres: Deciphering the Ends of DNA

by Catherine Brady

If Cech had provided the precedent for a catalytic action that relied on an RNA template, Blackburn and Greider’s hypothesis still flew in the face of accepted dogma: a central tenet of molecular biology at the time held that in the essential cellular mechanisms of eukaryotes, enzymes copied DNA into RNA, and never the reverse. The only exceptions found had occurred in then obscure retroviruses, which copied RNA into DNA (hence the term “retro”; HIV later became the most notorious of these viruses), thanks to the action of reverse transcriptase enzymes. Such enzymes were thought to hark back to earlier, more primitive life-forms, and biologists assumed that these enzymes did not exist in more complex organisms, which evolved later, with protein polymerases taking over the role played by RNA in synthesizing the genetic material of the cell. Making Blackburn and Greider’s hypothesis still more risky, reverse transcriptase typically copied thousands of nucleotides at a time in a viral genome. No reverse transcriptase had ever been found to copy only a short sequence of DNA.