Szathmáry E
Department of Plant Taxonomy and Ecology, Eötvös University, Budapest and Collegium Budapest, Szentháromság u. 2, H-1014 Budapest, Hungary.
Trends Genet. 1999 Jun;15(6):223-9. doi: 10.1016/s0168-9525(99)01730-8.
The genetic code, understood as the specific assignment of amino acids to nucleotide triplets, might have preceded the existence of translation. Amino acids became utilized as cofactors by ribozymes in a metabolically complex RNA world. Specific charging ribozymes linked amino acids to corresponding RNA handles, which could basepair with different ribozymes, via an anticodon hairpin, and so deliver the cofactor to the ribozyme. Growing of the 'handle' into a presumptive tRNA was possible while function was retained and modified throughout. A stereochemical relation between some amino acids and cognate anticodons/codons is likely to have been important in the earliest assignments. Recent experimental findings, including selection for ribozymes catalyzing peptide-bond formation and those utilizing an amino acid cofactor, hold promise that scenarios of this major transition can be tested.
遗传密码，即氨基酸与核苷酸三联体的特定对应关系，可能在翻译出现之前就已存在。在代谢复杂的RNA世界中，氨基酸被核酶用作辅助因子。特定的氨基酸负载核酶将氨基酸连接到相应的RNA“柄”上，该“柄”可通过反密码子发夹与不同的核酶进行碱基配对，从而将辅助因子传递给核酶。在功能得以保留并不断修饰的过程中，“柄”有可能演变成假定的转运RNA（tRNA）。在最早的对应关系中，某些氨基酸与同源反密码子/密码子之间的立体化学关系可能起到了重要作用。最近的实验发现，包括对催化肽键形成的核酶以及利用氨基酸辅助因子的核酶的筛选，为测试这一重大转变的各种情形带来了希望。
