A general two-step strategy to synthesize lariat RNAs.

We describe a general and efficient two-step strategy for lariat RNA synthesis. In the first step, a deoxyribozyme synthesizes 2',5'-branched RNA. In the second step, T4 RNA ligase closes the loop that completes the lariat. The loop-closure reaction can form either a natural or unnatural lariat isomer, depending on which of the two 3'-termini of the branched RNA reacts with the lone 5'-end. We demonstrate two approaches to control formation of either lariat isomer. In conjunction with other routes for lariat RNA synthesis, the two-step strategy described here will facilitate biochemical studies that require lariat RNAs of varying nucleotide sequence.