The Role of RNA and [4Fe/4S]2+/+ Iron Sulfur Clusters in the Biosynthesis of Deoxyribonucleotides
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Life is thought to have originated in an 'RNA World', where ribonucleic acids preceded DNA and proteins in the prebiotic milieu. This theory is based on, among other things, RNA's ability to both carry the genetic code and to affect rudimentary catalytic functions. We propose that RNA-based enzymes (ribozymes) catalyzed the early synthesis of DNA nucleotides using small peptides and metal cofactors. Redox-active cofactors such as iron-sulfur clusters have recently been shown to self-assemble within short peptide sequences. Beginning with a 16mer peptide that assembles a [4Fe/4S]<sup>2+/+</sup> cluster, we have designed two peptides, one that incorporates a biotin group and one with a lysine-tryptophan-lysine (KWK) DNA intercalation motif. Both modified peptides were shown to assemble [4Fe/4S]<sup>2+/+</sup> clusters under anaerobic conditions according to UV-visible spectroscopy and EPR data. By tethering the biotinylayted peptide to an agarose-strepavidin column, we can select an RNA molecule(s) from a large combinatorial pool that is capable of binding to the immobilized peptide-[4Fe/4S]<sup>2+/+</sup> complex. These studies may provide insight into the existence of metal-binding RNA molecules capable of generating the basic building blocks of DNA, thus providing a link between the ancient RNA world and modern living organisms.