Montmorillonite Catalysis of 30–50 Mer Oligonucleotides: Laboratory Demonstration of Potential Steps in the Origin of the RNA World

Elongation of the primer 32pdA(pdA)8pA proceeds by thereaction of the 5′-phosphorimidazolides of adenosine and uridine in the presence of montmorillonite clay. Daily addition of the activated nucleotides for up to 14 days results in theformation of 40–50 mers using the 5′-phosphorimidazolide of adenosine (ImpA) and 25–30 mers using the 5′-phosphorimidazolide of uridine (ImpU). The limitation on thelengths of the chains formed is not due to the inhibitors formedsince the same chain lengths were formed using 2–3 times the amount of montmorillonite catalyst. The shorter oligomers formedby the addition of U monomers is not due to its greater rate ofdecomposition since it was found that both the A and the U adducts decompose at about the same rates. Alkaline phosphatase hydrolysis studies revealed that some of the oligomers are cappedat the 5′-end to form, with ImpA,Ap32pdA(pdA)8pA(pA)n. The extent of capping depends on the reaction time and the purine or pyrimidine base inthe activated mononucleotide. Hydrolysis with ribonuclease T2 followed by alkaline phosphatase determined the sites ofthe 3′, 5′- and 2′, 5′-phosphodiester bonding to the primer. The potential significance of the mineral catalyzed formation of 50 mer oligonucleotides to the origin of life basedon RNA (the RNA world scenario) is discussed.

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