Evolution of a T7 RNA polymerase variant that transcribes 2′-O-methyl RNA


Modified RNA and DNA molecules have novel properties that their natural counterparts do not possess, such as better resistance to degradation in cells and improved pharmacokinetic behavior1,2. In particular, modifications at the 2′-OH of ribose are important for enhancing the stability of RNA3,4. Unfortunately, it is difficult to enzymatically synthesize modified nucleic acids of any substantial length because natural polymerases incorporate modified nucleotides inefficiently. Previously, we reported an activity-based method for selecting functional T7 RNA polymerase variants based on the ability of a T7 RNA polymerase to reproduce itself5. Here, we have modified the original procedure to identify polymerases that can efficiently incorporate multiple modified nucleotides at the 2′ position of the ribose. Most important, our method allows the selection of polymerases that have good processivities and can be combined to simultaneously incorporate several different modified nucleotides in a transcript.

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Figure 1: Autogene selection for active T7 RNA polymerase variants.
Figure 2: Polymerase activities with multiple 2′-O-methyl modifications and synthesis of long and complex modified transcripts using the selected polymerases.
Figure 3: Assays demonstrating the fidelity of the mutant enzyme, 'RGVG', E593G, V685A and the resistance of the 2′-O-methyl-modified RNA to cleavage by nucleases.


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This work was supported by a grant from the Office of Naval Research and by the Robert A. Welch Foundation.

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Correspondence to Andrew D Ellington.

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