Researchers at the University of California, San Diego, have shown that a crucial enzyme in cells can accurately "read" an expanded genetic alphabet with eight letters—twice the four letters found in all known life on Earth. This enzyme, called RNA polymerase, normally reads DNA and creates RNA, the first step in gene expression. In this study, scientists used a combination of biochemical experiments and high-resolution cryo-electron microscopy to observe how RNA polymerase from Escherichia coli (E. coli) bacteria interacts with two synthetic, or man-made, base pairs. These artificial genetic letters are not found in nature but were designed to mimic the function of natural DNA components. The detailed images captured by the researchers revealed that RNA polymerase recognizes these synthetic DNA letters using many of the same biochemical and structural signals it uses for natural base pairs. This discovery helps explain how the enzyme can accurately copy information written in an expanded genetic alphabet. In a related study published in the Proceedings of the National Academy of Sciences (PNAS), the same research team found that RNA polymerase can also recognize another pair of synthetic base pairs, even though these pairs lack the hydrogen bonds that typically help hold natural DNA base pairs together. These findings suggest that cells might be able to use their existing molecular machinery to handle synthetic genetic information. This research has implications beyond basic science. Earlier studies have already used expanded genetic alphabets to create synthetic DNA molecules that can recognize liver cancer cells. By providing a detailed molecular view of how RNA polymerase reads and transcribes non-natural DNA letters, this new research lays the groundwork for technologies based on expanded genetic codes. Potential applications include new diagnostic tools, therapies, and engineered biological systems with capabilities not found in nature. The study titled "Structural Basis of Transcription of the Hachimoji Eight-Letter Alphabet by E. coli RNA Polymerase," led by Dong Wang, PhD, a professor at the UC San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences, was published on September 2, 2026, in Nature Communications. A related study titled "Hydrophobic unnatural base pair promotes trigger loop closure and catalysis in cellular RNA polymerase independent of hydrogen bonding," also led by Wang, was published on August 12, 2026, in PNAS.