Illangasekare M, Yarus M
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347, USA.
Proc Natl Acad Sci U S A. 1999 May 11;96(10):5470-5. doi: 10.1073/pnas.96.10.5470.
RNA 77, derived by selection amplification, accelerates its own conversion to Phe-RNA (relative to randomized RNA) more than 6 x 10(7)-fold, by using amino acid adenylates as substrate. A modified assay system allows measurement of slow rates of aa-RNA formation, which for disfavored amino acid substrates can be more than 10(4)-fold slower than phenylalanine. Thus unlike previously characterized self-aminoacylators, RNA 77 catalysis is highly amino acid selective. Remarkably, both rates of aminoacyl transfer and amino acid specificities are greater for RNA 77 than measured for protein PheRS. These data experimentally support the possible existence of an ancestral amino acid-specific translation system relying entirely on RNA catalysis. RNA 77 itself embodies a possible transitional evolutionary state, in which side-chain-specific aa-RNA formation and anticodon-codon pairing were invested in the same molecule.
通过选择扩增获得的RNA 77，以氨基酸腺苷酸为底物，相对于随机RNA，其自身向苯丙氨酸RNA（Phe-RNA）的转化加速了超过6×10⁷倍。一种改进的检测系统能够测量氨基酸RNA形成的缓慢速率，对于不被青睐的氨基酸底物，其速率比苯丙氨酸慢超过10⁴倍。因此，与先前表征的自氨基酰化剂不同，RNA 77催化具有高度的氨基酸选择性。值得注意的是，RNA 77的氨基酰转移速率和氨基酸特异性都比蛋白质苯丙氨酰-tRNA合成酶（PheRS）测得的更高。这些数据通过实验支持了可能存在完全依赖RNA催化的祖先氨基酸特异性翻译系统。RNA 77本身体现了一种可能的过渡进化状态，其中侧链特异性氨基酸RNA的形成和反密码子-密码子配对存在于同一分子中。
