Catalytic Synthesis of Polyribonucleic Acid on Prebiotic Rock Glasses

Abstract

Reported here are experiments that show that ribonucleoside triphosphates are converted to polyribonucleic acid when incubated with rock glasses similar to those likely present 4.3-4.4 billion years ago on the Hadean Earth surface, where they were formed by impacts and volcanism. This polyribonucleic acid averages 100-300 nucleotides in length, with a substantial fraction of 3',-5'-dinucleotide linkages. Chemical analyses, including classical methods that were used to prove the structure of natural RNA, establish a polyribonucleic acid structure for these products. The polyribonucleic acid accumulated and was stable for months, with a synthesis rate of 2 × 10^-3 pmoles of triphosphate polymerized each hour per gram of glass (25°C, pH 7.5). These results suggest that polyribonucleotides were available to Hadean environments if triphosphates were. As many proposals are emerging describing how triphosphates might have been made on the Hadean Earth, the process observed here offers an important missing step in models for the prebiotic synthesis of RNA.

Keywords: Impact glasses; Mafic rocks; Nucleoside triphosphates; Origin of life; Prebiotic chemistry; RNA world.

FIG. 1.

NTPs polymerization on diabase glass. Incubation of all four nucleoside triphosphates (3 μM each, with [α-³²P]GTP) on five types of glass (22 mg) for 20 h, 25°C. Reaction supernatants (Sup) and urea washes (Urea) for each glass were loaded on a 20% denaturing PAGE. H₂O: control reaction in the absence of glass. NEPETop^-OH: partial alkaline hydrolysis of a 14-mer RNA molecule. Sizes in nucleotides are on the left. AGV, andesite; BRP, basalt; GSM, gabbro; MRM, diabase; NKT, nephelinite.

FIG. 2.

Time course of triphosphate polymerization on diabase glass. Left: Time course followed by PAGE (20%, 7 M urea) using labeled [α-³²P]GTP. Incubation times in lanes are indicated as minutes (′) and hours (h). Ladders are from partial hydrolysis of a 5′-labeled RNA 14-mer (left) and 31-mer (right); fragment lengths are in nucleotides. Color-coded numbers correspond to graph, showing cpm incorporated as a function of time for the 10 bands. Initial velocities in pmoles/min reflect material formed per milligram of glass, as calculated from the specific activity of the labeled GTP. Scintillation counting readings were performed in triplicate for each band on duplicated kinetic experiments. Error bars represent the mean of six values. cpm, counts per minute.

FIG. 3.

Ultrafiltration of polyribonucleic acid formed on diabase. Shown are starting material (S), filter eluates (E), and filter retentates (R) with increasing MWCO filters. K = kDa. NEPETop and 31RA: partial alkaline hydrolysis of 14-mer and 31-mer RNA molecules. Sizes in nucleotides are on the sides. Twenty percent PAGE, 7M urea. MWCO, molecular weight cutoff.

FIG. 4.

3D-Diode Array HPLC of products obtained by ammonia hydrolysis of polyribonucleic acid synthesized on diabase glass. (A) Hydrolyzed products of oligomerization for polyribonucleic acid made from all four standard nucleotides. (B) Control mixture of 2′ and 3′-nucleotide monophosphate. Peak assignments were confirmed by HPLC runs of treated and nontreated NMPs and by matching spectrum profiles for controls and samples (Supplementary Figs. S19 and S20, and data not shown). The major peak in [A] running at ∼6 min, resulting from the degradation of ATP input material, masks the peaks from 2′ and 3′UMP. The presence of lines corresponding to UMP peaks can be detected in the 3D view (Supplementary Fig. S22) and was confirmed with the analysis of single-nucleotide UTP-oligomerization reactions (Supplementary Fig. S23). Far-left peaks in [A] come from residual open-ring nucleosides from previous HPLC (Methods section in Supplementary Data; Supplementary Fig. S19). Right-tilted and front views are shown in Supplementary Figure S21. Color shading is added for emphasis.

FIG. 5.

Ribonuclease ONE™ digestions of diabase glass-formed poyribonucleic acid. Time course of Ribonuclease ONE digestions of oligomerization products on diabase for single nucleotide triphosphates (A, C, G, U) and a mixture of the four (NTPs). NEPETop and 31RA: partial alkaline hydrolysis of 14-mer and 31-mer RNA molecules. Sizes in nucleotides are on the sides. Twenty percent PAGE, 7 M urea.