Alignment of eukaryotic class II RNRs plus a few representative monomeric and dimeric prokaryotic class II RNRs. The portion of the alignment shown here illustrates presence of the dimer interface-mimicking domain in monomeric enzymes and absence from dimeric class II RNR enzymes (top five sequences). The domain mimics the dimer interface, where the substrate specificity effector binds . All eukaryotic proteins (P. ramorum, P. sojae, D. discoideum, E. gracilis and M. brevicollis) except the T. vaginalis sequence carry the insert, indicating they are monomeric. In support of this, the P. ramorum structure could not be modelled with the dimeric T. maritima structure using Swiss Model . Nor could we model the T. vaginalis sequence with the L. lactobacillus structure, whereas the opposite combinations (P. ramorum with L. lactobacillus and T. vaginalis with T. maritima) successfully produce structure models (data not shown).