Catalyzes the synthesis of alpha-ribazole-5'-phosphate from nicotinate mononucleotide (NAMN) and 5,6-dimethylbenzimidazole (DMB). 5,6-dimethylbenzimidazole + nicotinate beta-D-ribonucleotide = alpha-ribazole 5'-phosphate + H(+) + nicotinate Nucleoside biosynthesis; alpha-ribazole biosynthesis; alpha-ribazole from 5,6-dimethylbenzimidazole: step 1/2. Homodimer. Belongs to the CobT family. Was originally thought to originate from Pseudomonas denitrificans, but similarity searches show that the sequence is much closer to Sinorhizobium. The entry's taxonomy has been changed.