This domain is found to the N terminus of the ribonucleotide reductase barrel domain (IPR000788). It occurs in bacterial class II ribonucleotide reductase proteins which depend upon coenzyme B12 (deoxyadenosylcobalamine) [1].
Borovok I, Kreisberg-Zakarin R, Yanko M, Schreiber R, Myslovati M, Aslund F, Holmgren A, Cohen G, Aharonowitz Y.
Streptomyces spp. contain class Ia and class II ribonucleotide reductases: expression analysis of the genes in vegetative growth.
Microbiology (Reading, Engl.) 148 391-404 2002
[PubMed: 11832503] http://mic.sgmjournals.org/cgi/content/abstract/148/2/391