Cellular conditions of weakly chelated magnesium ions strongly promote RNA stability and catalysis

Most RNA folding studies have been performed under non-physiological conditions of high concentrations (≥10 mM) of Mg²⁺_free, while actual cellular concentrations of Mg²⁺_free are only ~1 mM in a background of greater than 50 mM Mg²⁺_total. To uncover cellular behavior of RNA, we devised cytoplasm mimic systems that include biological concentrations of amino acids, which weakly chelate Mg²⁺. Amino acid-chelated Mg²⁺ (aaCM) of ~15 mM dramatically increases RNA folding and prevents RNA degradation. Furthermore, aaCM enhance self-cleavage of several different ribozymes, up to 100,000-fold at Mg²⁺_free of just 0.5 mM, indirectly through RNA compaction. Other metabolites that weakly chelate magnesium offer similar beneficial effects, which implies chelated magnesium may enhance RNA function in the cell in the same way. Overall, these results indicate that the states of Mg²⁺ should not be limited to free and bound only, as weakly bound Mg²⁺ strongly promotes RNA function under cellular conditions.