In E. coli promoter there are two consensus sequence which is located upstream to from the start site of the transcription. One consensus sequence is present at -10 and one at -35.
These consensus sequences are necessary to be recognized to start the transcription. It is recognized by the sigma factor which is a part of RNA polymerase. After recognition transcription starts.
The termination of transcription occurs by a rho protein. Rho is ATP dependent RNA stimulated helicase which disrupts the complex of RNA-DNA and terminates transcription.
