Abstract
All organisms employ a family of enzymes called ribonucleotide reductases (RNRs) to generate deoxyribonucleotides from their ribose counterparts. Class II RNRs utilize a cofactor derived from Vitamin B12 to carry out this complex reduction reaction. However, a conundrum arises because it is difficult to superimpose the RNR system upon the varying simplicities of early primordial conditions: if DNA (gene sequences are necessary for successful construction of modern multi-unit RNR complexes, yet RNRs are necessary for DNA production, which came first? Therefore, we propose that ancient RNA sequences existed which may have catalyzed the same reaction using B12 as a reduction/oxidation cofactor. A random ssDNA library was synthesized for selection of RNAs that bind to B12 in a system convenient for electrochemical analysis. A dsDNA PCR product was transcribed in vitro and a portion of the RNA taken through seven rounds of the SELEX algorithm. Sequencing of representative clones from the final candidate pool has revealed at least 5 unique clone families. Following characterization of these clones, gold electrode analysis will be performed on the RNA-B12 complex to detect the reduction potential of the Cobalt metal center. The ability of RNA to fine tune metal cofactors would be an interesting and important item of support for the 'RNA World' and our own RNA-RNR hypothesis.
