Chiral-selective aminoacylation of an RNA minihelix.

Amino acids in natural proteins have a chiral, asymmetric center at the alpha carbon that is of the L-configuration. The sugar backbone of natural RNAs are also homochiral, but of the D-configuration. Because protein synthesis requires the aminoacylation of RNA, it is this step that could have provided chiral selectivity. Here we show that an RNA minihelix was aminoacylated by an aminoacyl-phosphate-D-oligonucleotide with a clear preference for L- as opposed to D-amino acids. A mirror-image RNA system showed the opposite selectivity. These results suggest the possibility that the selection of L-amino acids for proteins was determined by the stereochemistry of RNA.