This family of proteins represent the nicotinate-nucleotide- dimethylbenzimidazole phosphoribosyltransferase (NN:DBI PRT) enzymes involved in dimethylbenzimidazole synthesis. This function is essential to de novo cobalamin (vitamin B12) production in bacteria. Nicotinate mononucleotide (NaMN):5,6-dimethylbenzimidazole (DMB) phosphoribosyltransferase (CobT) from Salmonella enterica plays a central role in the synthesis of alpha-ribazole-5'-phosphate, an intermediate for the lower ligand of cobalamin.