GENERATION OF THE GLYCYL RADICAL OF THE ANAEROBIC ESCHERICHIA-COLI RIBONUCLEOTIDE REDUCTASE REQUIRES A SPECIFIC ACTIVATING ENZYME

The anaerobic ribonucleotide reductase from Escherichia coli contains a glycyl radical as part of its polypeptide structure. The radical is generated by an enzyme system present in E. coli. The reductase is cod ed for by the nrdD gene located at 96 min. Immediately downstream, we now find an open reading frame with the potential to code for a 17.5-k Da protein with sequence homology to a protein required for the genera tion of the glycyl radical of pyruvate formate lyase, The protein corr esponding to this open reading frame is required for the generation of the glycyl radical of the anaerobic reductase and binds tightly to th e reductase, The ''activase'' contains iron, required for activity, Th e general requirements for generation of a glycyl radical are identica l for the reductase and pyruvate formate lyase. For the reductase, the requirement of an iron-containing activase suggests the possibility t hat the iron-sulfur cluster of the enzyme is not involved in radical g eneration but may participate directly in the reduction of the ribonuc leotide.