The RNA oligomers (3-5 mer) are expanded for various compositions, in which the concentrations (top) of the oligomers in the absence (grey) and presence (blue) of valine are presented. The blue trace represents random oligomerisation, where all nucleotides are assumed to have equal efficiency. The distribution ratio of the oligomers is adjusted based on the total yield of the n-mers in the performed reaction. The bottom plot shows the relative yield (fold increase) for each sequence composition. In the experiments, 40 mM cyclic nucleotides and 100 mM valine at pH 10 and 50 l were rapidly dried and incubated for 20 h at 25 C. The quantifications were done by LC-MS and a self-written LabVIEW programme. The results are the mean with S.D. of three independent experiments, and we show the largest S.D. in each data set (complete errors in Figs. S25a and S31 ). The isotopic distribution AAAAA and GGGCC is identical, and both concentrations are assumed equal, marked by * in ( e ). All isotope fits are given in Supplementary Data 3 . Source data are available for all panels ( a - e ).
