Structural origins of RNA polymerase open promoter complex stability.

The first step in gene expression in all organisms requires opening the DNA duplex to expose one strand for templated RNA synthesis. In , promoter DNA sequence fundamentally determines how fast the RNA polymerase (RNAP) forms "open" complexes (RPo), whether RPo persists for seconds or hours, and how quickly RNAP transitions from initiation to elongation. These rates control promoter strength in vivo, but their structural origins remain largely unknown.