An unnatural base pair for efficient incorporation of nucleotide analogs into RNAs.

An unnatural base, 2-amino-6-(2-thiazolyl)purine (denoted as v), was developed as an efficient complementary base of another unnatural base, 2-oxo(1H)pyridine (denoted as y). The nucleoside derivatives of v and DNA fragments containing v were chemically synthesized. The efficiency and selectivity of the v-y pairing in replication and transcription were examined and compared to those of a previously developed unnatural base pair between 2-amino-6-(2-thienyl)purine (s) and y. The nucleoside 5'-triphosphate of y (dyTP or yTP) was selectively and efficiently incorporated into DNA or RNA opposite v. The efficiency of the v-y pairing was much higher than that of the s-y pairing. The unnatural v-y pair could be useful for large-scale preparations of RNA molecules containing unnatural bases at desired positions for the expansion of the genetic alphabet.