In a story of scientific discovery, David Liu shares a breakthrough: his lab’s development of base editors that can rewrite DNA. This crucial step in genome editing takes the promise of CRISPR to the next level: if CRISPR proteins are molecular scissors, programmed to cut specific DNA sequences, then base editors are pencils, capable of directly rewriting one DNA letter into another. Learn more about how these molecular machines work — and their potential to treat or even cure genetic diseases.