Chemical copying
of RNA template 3′-GCCC into 3′-NP-DNA
using (A) 3′-NH2-2AIpddC alone, (B) 3′-NH2-2AIpddC and 3′-NH2-5′-PO3-ddG, and (C) 3′-NH2-2AIpddC and 3′-NH2-2AIpddG. The nucleotide highlighted in red indicates the
3′-NH2-ddC at the end of the primer. All primer
extension reactions were conducted at pH 8.5, 25 °C, and 200
mM Na+-bicine with 10 mM of each mononucleotide and 50
mM Mg2+. Reaction products were analyzed by polyacrylamide
gel electrophoresis (PAGE). The RNA templating region is indicated
in blue. The slow primer extension observed in the presence of 3′-NH2-2AIpddC alone (t1/2 = 16 ±
1 min), or 3′-NH2-2AIpddC plus 3′-NH2-ddG-5′-monophosphate (t1/2 = 26 ± 2 min) relative to 3′-NH2-2AIpddC
plus 3′-NH2-2AIpddG (t1/2 < 0.5 min) suggests that the polymerization reaction proceeds
via the imidazolium-bridged dinucleotide intermediate C-2AI-G. P,
primer. Cyt, cytosine. Gua, guanine.