Scientists have determined the three-dimensional structure of the transcription initiation complex, the key intermediate in the process by which cells read out genetic information in DNA. The “molecular machine” responsible for transcription initiation — a protein complex that consists of the enzyme RNA polymerase and the initiation factor sigma — recognizes a specific site on DNA preceding a gene, binds to DNA, unwinds the DNA helix, and pre-organizes the unwound DNA to enable subsequent reactions.