Mechanism of Transcription Arrest By The Nun Protein of Bacteriophage HK022

Transcription elongation is universally subject to regulatory factors that alter the rate and processivity of gene expression (Roberts et al, 2008). Escherichia coli RNA polymerase (RNAP) and its auxiliary transcription factors have long been studied as a model for understanding regulation of elongation, but biochemical insights into some of these mechanisms still must be elucidated. In this study I explored the mechanism of transcription modification by the Nun protein of phage HK022. I demonstrated that Nun is novel in its ability to both activate and arrest transcription by the same mechanism of inhibiting lateral movement of RNAP on DNA template. I provided evidence that Nun targets the upstream end of the transcription bubble to stabilize the translocation state of RNAP, and that intrinsic translocation bias of RNAP directly influences whether Nun activates or arrests transcription.