A promiscuous ribozyme promotes nucleotide synthesis in addition to ribose chemistry

Here we report the in vitro selection of an unusual ribozyme that efficiently performs nucleotide synthesis even though it was selected to perform a distinctly different sugar chemistry. This ribozyme, called pR1, when derivatized with ribose 5-phosphate (PR) at its 3' terminus and incubated with 6-thioguanine, produces two interconverting thiol-containing products corresponding to a Schiff base and its Amadori rearranged product. Consistent with this hypothesis, removing the 2-hydroxyl from the PR substrate results in only a single product. Surprisingly, as this was not selected for, switching the tethered PR substrate to 5-phosphoribosyl 1-pyrophosphate results in the synthesis of 6-thioguanosine 5'-monophosphate. The discovery that a ribozyme can promote such distinct reactions spontaneously demonstrates that an RNA-mediated metabolism early in evolution could have evolved important new functionalities via ribozyme promiscuity.