Dr. LENG Fenfei
Associate Professor of Biochemistry
Department of Chemistry & Biochemistry
Florida International University, USA

Date: Wed, 9-August-2017 (updated)
Time: 4:00 PM (updated)
Venue: Room A2-08, Mrs Chen Yang Foo Oi Telemedicine Centre 
2/F, William MW Mong Block, Faculty of Medicine Building 
21 Sassoon Road, Pokfulam, Hong Kong

Summary:
Transcription can induce localized DNA supercoiling in vitro and in vivo. This phenomenon can be explained by a "twin-supercoiled-domain" model of transcription where (+) supercoils are produced in front of the RNA polymerase and (-) supercoils behind it. However, how transcription-coupled DNA supercoiling (TCDS) at the molecular level is regulated has not been fully understood. After over a decade studies in our laboratory, now we start to understand what parameters regulate the localized TCDS in vitro and in vivo. For instance, using defined protein systems, we demonstrated that a variety of DNA-binding proteins are able to form topological barriers and facilitate a twin-domain mechanism to enhance TCDS. These DNA-binding proteins are able to divide a supercoiled DNA molecule into two independent topological domains. Using specifically designed plasmids and E. coli strains, we showed that TCDS is dependent on the on the length of RNA transcripts in vivo, precisely predicted by the twin-supercoiled-domain model of transcription. We also demonstrated that TCDS is dependent on the promoter strength and does not require anchoring of DNA to the bacterial cytoplasmic membrane. These results indicate that a transcribing RNA polymerase alone is sufficient to cause a change in local DNA superhelicity. Recently, using genetic approaches, we showed that transient and dynamic (-) TCDS is able to potently activate the supercoiling-sensitive promoter Pleu-500 in vivo. TCDS can be generated on topologically open DNA molecules, i.e. linear DNA molecules in E. coli. These results suggest that topological boundaries or barriers are not required for the production of TCDS in vivo.

ALL ARE WELCOME