抄録
The temperature dependence of pseudo-first-order rate constants (kcyc) of the cyclization of hexanucleotides 5'-d(pGCGCG)rC and 5'-d(pGCCCG)rG was investigated in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC) and imidazole at 0 - 75 ℃. Although the association between the elongating oligomer and the activated monomer is necessary for the success of the formation of oligonucleotides on a polynucleotide template or a clay catalyst, the phosphodiester bond formation in the case of cyclization readily occurs without these catalysts. Thus, the cyclization is regarded as a simple model of the formation of phosphodiester bond. The rate constants (kcyc) were compared with those of the cleavage of the ribose phosphodiester bond, in which the cyclization was more than 50 times faster than the cleavage at 75 ℃. On the basis of this fact, it is deduced that the prebiotic formations of RNA oligomers such as the template-directed reaction and the mineral catalyzed oligomerization would be possible at high temperatures if the association between elongating oligomer and activated monomer (or activated oligomer) is sufficiently strong.
