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. 2000 Apr 11;97(8):3868-71.
doi: 10.1073/pnas.97.8.3868.

Peptide nucleic acids rather than RNA may have been the first genetic molecule

K E Nelson  1 , M Levy, S L Miller
Collaborators, Affiliations

Peptide nucleic acids rather than RNA may have been the first genetic molecule

K E Nelson et al. Proc Natl Acad Sci U S A. .

Abstract

Numerous problems exist with the current thinking of RNA as the first genetic material. No plausible prebiotic processes have yet been demonstrated to produce the nucleosides or nucleotides or for efficient two-way nonenzymatic replication. Peptide nucleic acid (PNA) is a promising precursor to RNA, consisting of N-(2-aminoethyl)glycine (AEG) and the adenine, uracil, guanine, and cytosine-N-acetic acids. However, PNA has not yet been demonstrated to be prebiotic. We show here that AEG is produced directly in electric discharge reactions from CH(4), N(2), NH(3), and H(2)O. Electric discharges also produce ethylenediamine, as do NH(4)CN polymerizations. AEG is produced from the robust Strecker synthesis with ethylenediamine. The NH(4)CN polymerization in the presence of glycine leads to the adenine and guanine-N(9)-acetic acids, and the cytosine and uracil-N(1)-acetic acids are produced in high yield from the reaction of cyanoacetaldehyde with hydantoic acid, rather than urea. Preliminary experiments suggest that AEG may polymerize rapidly at 100 degrees C to give the polypeptide backbone of PNA. The ease of synthesis of the components of PNA and possibility of polymerization of AEG reinforce the possibility that PNA may have been the first genetic material.

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Figures

Figure 1
Figure 1
In peptide nucleic acids, the ribose phosphate backbone is replaced with a polyamide backbone of N-(2-aminoethyl)glycine (AEG or ED monoacetic acid), and the four bases are connected through an acetic acid linker.
Figure 2
Figure 2
A proposed mechanism for production of ED and 2,3-diaminopropionic acid from NH4CN and HCN trimer with consequent production of cyanogen from higher HCN oligomers.
Figure 3
Figure 3
Yield of AEG versus time for the reaction of 10−1 to 10−4 M ED, HCN, and H2CO at 25°C and pH 7 after acid hydrolysis. The yields of AEG decline after 5 days because of the formation of ethylenediamine diacetic acid.
Figure 4
Figure 4
A proposed mechanism for the production of the purine-N9-acetic acids from HCN and glycine.
See this image and copyright information in PMC

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