Stribling R, Miller S L
Department of Chemistry, University of California, San Diego, La Jolla 92093, USA.
J Mol Evol. 1991;32:289-95. doi: 10.1007/BF02102186.
One of the most important sets of model prebiotic experiments consists of reactions that synthesize complementary oligonucleotides from preformed templates under nonenzymatic conditions. Most of these experiments are conducted at 4 degrees C using 0.01-0.1 M concentrations of activated nucleotide monomer and template (monomer equivalent). In an attempt to extend the conditions under which this type of reaction can occur, we have concentrated the reactants by freezing at -18 degrees C, which is close to the NaCl-H2O eutectic at -21 degrees C. The results from this set of experiments suggest that successful syntheses can occur with poly(C) concentrations as low at 5 x 10(-4) M and 2MeImpG concentrations at 10(-3) M. It was also anticipated that this mechanism might allow the previously unsuccessful poly(A)-directed synthesis of oligo(U)s to occur. However, no template effect was seen with the poly(A) and ImpU system. The failure of these conditions to allow template-directed synthesis of oligo(U)s supports the previously proposed idea that pyrimidines may not have been part of the earliest genetic material. Because of the low concentrations of monomer and template that would be expected from prebiotic syntheses, this lower temperature could be considered a more plausible geologic setting for template-directed synthesis than the standard reaction conditions.
最重要的一组模拟益生元实验包括在非酶促条件下从预先形成的模板合成互补寡核苷酸的反应。这些实验大多在4℃下进行，使用0.01 - 0.1M浓度的活化核苷酸单体和模板（单体当量）。为了扩展这种反应能够发生的条件，我们通过在-18℃冷冻来浓缩反应物，-18℃接近-21℃时的NaCl - H₂O共晶点。这组实验的结果表明，当聚（C）浓度低至5×10⁻⁴M且2 - 甲基肌苷鸟苷（2MeImpG）浓度为10⁻³M时，也能成功合成。还预计这种机制可能使以前未成功的聚（A）指导的寡聚（U）合成得以发生。然而，在聚（A）和肌苷尿苷（ImpU）系统中未观察到模板效应。这些条件未能实现模板指导的寡聚（U）合成，支持了先前提出的观点，即嘧啶可能不是最早遗传物质的一部分。由于益生元合成预期的单体和模板浓度较低，与标准反应条件相比，这种较低温度可被视为模板指导合成更合理的地质环境。
