Craig T. Martin & Olga S. Mironova, Wiley Encyclopedia of Chemical Biology, Vol 4 (Editor: Tadhg P. Begley), 584-595, 2009.
Initiation of transcription is a complex process, requiring melting of the DNA duplex at a sequence-defined location, de novo synthesis of an initial dinucleotide, polymerization/growth from that dinucleotide to a larger oligonucleotide in an extended RNA-DNA hybrid, displacement and threading of the 5′ end of the RNA into an exit channel, and release of the initial promoter contacts. These events are necessarily driven energetically by growth of the RNA-DNA hybrid. It has long been expected and is now becoming structurally clear that stress inherent in this transformation leads to instability during this phase and is a source of the abortive release of short RNA products that is characteristic of RNA polymerases. That apparently unrelated single and multisubunit RNA polymerases share extensive mechanistic (but not structural) homology, likely reflects the demands of the process.