The circular dichroism of synthetic ribonucleic acids and the influence of uracil on conformation

We present CD spectra of four trinucleoside diphosphates, UpUpG, GpUpG, ApUpA, and ApUpG, of four single‐stranded polymers, poly AC, poly GU, poly AU, and poly AdU, and of five double‐stranded polymers, poly A:U, poly G:C, poly AU:AU, poly AdU:AdU, and poly GC:GC. The measured spectra are compared with empirical firstneighbor calculations. Our results, taken together with data from the literature, suggest that UpA and UpG sequences are relatively unstacked in a single‐stranded RNA compared with these isolated dimers in solution. These sequences may influence the structure and function of natural RNAs. Our results on double‐stranded RNAs indicate that the spectral changes which occur upon formation of a double helix are unique to the type of base pair involved and are relatively independent of sequence.