Transcription Termination and Its Control in E. coli

Abstract

INTRODUCTION
The transcription of DNA in E. coli is bounded by both initiation and termination sites. Although many terminators must serve as permanent boundaries of transcription units, it is becoming apparent that they also may be sites at which positive control of transcription occurs, executed by specific regulators that allow RNA polymerase to ignore terminators and synthesize mRNA for regions beyond them. This review will consider the occurrence of termination in vivo and in vitro, the enzymology of termination and the involvement of transcription termination in genetic control.

TERMINATION IN VITRO
Although there is no doubt that transcription in E. coli terminates at specific sites, it is difficult to demonstrate this solely by examining RNA isolated from the cell. One cannot conclude rigorously that termination has occurred merely if RNA for the region beyond a putative terminator is absent since the transcript might be too unstable to detect. The existence of processing of both messenger and stable RNA further complicates the identification of transcription units from RNA molecules that are found in the cell. The most direct evidence that specific termination occurs in vivo is that several transcripts isolated from cells have identical counterparts arising from transcription termination in vitro. Thus I will consider termination in vivo mainly in reference to studies with purified components in vitro.

Transcription by purified RNA polymerase obviously terminates, since the usual enzymatic reaction ends after a fraction of an hour and yields some discrete species in the RNA product. In general, this termination is...