rRNA Transcription in Escherichia coli

Ribosomal RNA transcription is the rate-limiting step in ribosome synthesis in bacteria and has been investigated intensely for over half a century. Multiple mechanisms ensure that rRNA synthesis rates are appropriate for the cell's particular growth condition. Recently, important advances have been made in our understanding of rRNA transcription initiation in Escherichia coli. These include (a)a model at the atomic level of the network of protein-DNA and protein-protein interactions that recruit RNA polymerase to rRNA promoters, accounting for their extraordinary strength; (b)discovery of the nonredundant roles of two small molecule effectors, ppGpp and the initiating NTP, in regulation of rRNA transcription initiation; and (c)identification of a new component of the transcription machinery, DksA, that is absolutely required for regulation of rRNA promoter activity. Together, these advances provide clues important for our molecular understanding not only of rRNA transcription, but also of transcription in general.