Co 2+ binding RNA aptamers were chosen as research models to reveal the structural basis underlying the recognition of Co 2+ by RNA, with the application of two distinct methods. Using the nucleotide analog interfer-ence mapping assay, we found strong interference effects after incorpora-tion of the 7-deaza guanosine phosphorotioate analog into the RNA chain at equivalent positions G27 and G28 in aptamer no.