Every living cell transcribes DNA into RNA. This process begins when an enzyme called RNA polymerase (RNAP) clamps onto DNA. Within a few hundred milliseconds, the DNA double helix unwinds to form a node known as the transcription bubble, so that one exposed DNA strand can be copied into a complementary RNA strand. How RNAP accomplishes this feat is largely unknown. A snapshot of RNAP in the act of opening that bubble would provide a wealth of information, but the process happens too quickly for current technology to easily capture…
