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J Mol Biol. 2003 Jun 13;329(4):655-62.

Role of E.coli transcription-repair coupling factor Mfd in Nun-mediated transcription termination.

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Department of Microbiology and Institute of Cancer Research, College of Physicians and Surgeons, Columbia University, 701 West 168th Street, 9th Floor Rm 914, New York, NY 10032, USA.


Phage HK022 Nun protein excludes phage lambda by binding nascent lambda-nut RNA and inducing termination and transcript release. In contrast, in a purified in vitro system, Nun arrests transcription on lambdaDNA templates without dissociation of the transcription elongation complex (TEC). Our evidence indicates that transcription-repair coupling factor (Mfd) frees Nun-arrested RNA polymerase. The activity of Nun is enhanced in an mfd-null mutant, consistent with prolonged association of Nun with the TEC. Furthermore, expression of lambda nut RNA in the mfd mutant titrates Nun, allowing superinfecting lambda to form plaques. Finally, addition of Mfd releases a Nun-arrested transcription complex in vitro.

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