Structural basis of transcription of the hachimoji eight-letter alphabet by E. coli RNA polymerase.

E. coli RNA polymerase can efficiently transcribe an eight-letter genetic alphabet, including two orthogonal unnatural base pairs, with high fidelity and structural compatibility.

• Why it matters: Expanding genetic alphabets enhances nucleic acid diversity and potential molecular functions, but the compatibility of unnatural base pairs with cellular transcription machinery remains uncertain.
• What they did: The study synthesized a high-fidelity Z* analogue to reduce misincorporation and used cryo-electron microscopy to determine four structures of RNA polymerase incorporating unnatural base pairs at resolutions of 2.42–2.75 Å.
• The result: Findings demonstrate that E. coli RNA polymerase recognizes unnatural base pairs similarly to natural ones, confirming the feasibility of an eight-letter genetic alphabet for transcription and expanding possibilities for synthetic biology.