The mechanism by which informational
polymers first formed on the
early earth is currently unknown. The RNA world hypothesis implies
that RNA oligomers were produced prebiotically, before the emergence
of enzymes, but the demonstration of such a process remains challenging.
Alternatively, RNA may have been preceded by an earlier ancestral
polymer, or proto-RNA, that had a greater propensity for self-assembly
than RNA, with the eventual transition to functionally superior RNA
being the result of chemical or biological evolution. We report a
new class of nucleic acid analog, depsipeptide nucleic acid (DepsiPNA),
which displays several properties that are attractive as a candidate
for proto-RNA. The monomers of depsipeptide nucleic acids can form
under plausibly prebiotic conditions. These monomers oligomerize spontaneously
when dried from aqueous solutions to form nucleobase-functionalized
depsipeptides. Once formed, these DepsiPNA oligomers are capable of
complementary self-assembly and are resistant to hydrolysis in the
assembled state. These results suggest that the initial formation
of primitive, self-assembling, informational polymers on the early
earth may have been relatively facile if the constraints of an RNA-first
scenario are relaxed.