Insights into transcription: structure and function of single-subunit DNA-dependent RNA polymerases.

Single-subunit RNA polymerases are widespread throughout prokaryotic and eukaryotic organisms, and also viruses. T7 RNA polymerase is one of the simplest DNA-dependent enzymes, capable of transcribing a complete gene without the need for additional proteins. During the past two years, three illuminating crystal structures of T7 RNA polymerase complexed to either T7 lysozyme, which is a transcription inhibitor, an open promoter DNA fragment or a promoter DNA fragment being transcribed into RNA at initiation have been determined. For the first time, these structures describe in detail the intricate mechanism of transcription initiation by T7 RNA polymerase, which is likely to be a general model for other related RNA polymerases.