Monnard Pierre-Alain, Kanavarioti Anastassia, Deamer David W
Department of Chemistry and Biochemistry, University of California, 1156 High Street, Santa Cruz, California 95064, USA.
J Am Chem Soc. 2003 Nov 12;125(45):13734-40. doi: 10.1021/ja036465h.
The RNA world hypothesis requires a plausible mechanism by which RNA itself (or precursor RNA-like polymers) can be synthesized nonenzymatically from the corresponding building blocks. Simulation experiments have exploited chemically reactive mononucleotides as monomers. Solutions of such monomers in the prebiotic environment were likely to be very dilute, but in experimental simulations of polymerization reactions dilute solutions of activated mononucleotides in the millimolar range hydrolyze extensively, and only trace amounts of dimers and trimers are formed. We report here that random medium-size RNA analogues with mixed sequences (5- to 17-mers with traces of longer products) can be synthesized in ice eutectic phases that are produced when dilute solutions of activated monomers and catalysts (Mg(II) and Pb(II)) are frozen and maintained at -18 degrees C for periods up to 38 days. Under these conditions, the monomers are concentrated as eutectics in an ice matrix. Hydrolysis of the activated mononucleotides was suppressed at low-temperature ranges, and polymerization was enhanced with yields up to 90%. Analysis of the mixed oligomers established that incorporation of both purine and pyrimidine bases proceeded at comparable rates and yields. These results suggest that ice deposits on the early Earth could have facilitated the synthesis of short- and medium-size random sequence RNA analogues and thereby provided a microenvironment suitable for the formation of biopolymers or their precursors.
RNA世界假说需要一种合理的机制，通过该机制RNA自身（或类似RNA的前体聚合物）能够由相应的构件非酶促合成。模拟实验利用化学反应性单核苷酸作为单体。在益生元环境中，此类单体的溶液很可能非常稀释，但在聚合反应的实验模拟中，毫摩尔范围内的活化单核苷酸稀溶液会大量水解，仅形成痕量的二聚体和三聚体。我们在此报告，当活化单体和催化剂（Mg(II)和Pb(II)）的稀溶液冷冻并在-18℃下保持长达38天时所产生的冰共晶相中，可以合成具有混合序列的随机中等大小RNA类似物（5至17聚体，并伴有痕量的更长产物）。在这些条件下，单体作为共晶物浓缩在冰基质中。在低温范围内，活化单核苷酸的水解受到抑制，聚合作用增强，产率高达90%。对混合寡聚物的分析表明，嘌呤和嘧啶碱基的掺入以相当的速率和产率进行。这些结果表明，早期地球上的冰沉积物可能促进了短和中等大小随机序列RNA类似物的合成，从而提供了一个适合生物聚合物或其前体形成的微环境。
