Nature Structural Biology pp 293 - 300

Many biologists believe that RNA is the missing link in the evolutionary progression from primordial ooze to the DNA world. The key to understanding the link between RNA and DNA may be in an enzyme called ribonucleotide reductase (RNR), which converts ribonucleotides, the building blocks of RNA, into deoxyribonucleotides, the building blocks of DNA. A report in the April issue of Nature Structural Biology offers insight into the regulation and catalytic function of these enzymes and may offer clues to the relationship between the RNA world and the DNA world.

Using X-ray crystallography, Catherine Drennan and colleagues at the Massachusetts Institute of Technology, in Cambridge, Massachusetts, USA, have now determined the first structure of a class II ribonucleotide reductase. As it turns out, the structure of this monomeric class II enzyme has some similarities to the structures of the more complex, oligomeric class I and III enzymes. The structure also reveals for the first time the relationship between the active site, cofactor site and allosteric regulation site juxtaposed in a functionally intact RNR. The structure thus begins to address a long-standing question of how substrate recognition is regulated in these important enzymes.