GUEST COMMENTARY Gene-Specific Regulation by a Transcript Cleavage Factor: Facilitating Promoter Escape

The transcript cleavage factor GreA can play a significant role in stimulating the escape of RNA polymerase from native promoters in Escherichia coli. The bacterial Gre factors associate with RNA polymerase (RNAP) during transcription and induce cleavage of the nas-cent transcript at the active site of the enzyme (7, 17). Analysis with purified components in vitro has indicated that Gre fac-tors can mediate effects at multiple stages of the transcription cycle. During the elongation phase of transcription, Gre fac-tors can rescue stalled elongation complexes through their ability to stimulate endonucleolytic cleavage of the nascent RNA (1, 2). In addition, during the early stages of transcrip-tion, they can facilitate the process by which RNAP escapes the promoter and makes the transition to the elongation phase of transcription (6, 9, 28). While the Gre factors have been ex