Transcription elongation: structural basis and mechanisms.

A ternary complex composed of RNA polymerase (RNAP), DNA template, and RNA transcript is the central intermediate in the transcription cycle responsible for the elongation of the RNA chain. Although the basic biochemistry of RNAP functioning is well understood, little is known about the underlying structural determinants. The absence of high- resolution structural data has hampered our understanding of RNAP mechanism. However, recent work suggests a structure-function model of the ternary elongation complex, if not at a defined structural level, then at least as a conceptual view, such that key components of RNAP are defined operationally on the basis of compelling biochemical, protein chemical, and genetic data. The model has important implications for mechanisms of transcription elongation and also for initiation and termination.