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Edouard Bertrand - RNA polymerase II : how cells assemble it and get genes transcribed

Speaker : Edouard Bertrand - Institut de génétique humaine - UMR 5535 - CNRS - Montpellier

When : thursday 16 th May at 11 am

Where : Salle CO23 (grande salle de réunions du CBP rez-de-chaussée LR6)

Title :"RNA polymerase II : how cells assemble it and get genes transcribed"

RNA polymerase II is a key cellular enzyme, and much is known about transcription from biochemical and structural studies. Despite this, we know little about how cells produce this enzyme and how transcription occurs in living cells. We study transcription at the level of single cells using HIV-1 as a model system. The control of HIV-1 transcription is a key step in the viral cycle. It faces two opposite constrains : it must be very low during latency, and very strong during acute phase. Stochastic variations of transcriptional activity at the level of single cells, also called transcriptional noise, are known to influence the decision between latency and acute infection, by initiating or terminating the positive feed-back loop mediated by Tat. Transcription has been well-characterized at the biochemical level, but remains poorly understood at the level of single cells. We have developped tools that measure transcription of a single provirus in live single cells and in real-time. Using an optimized MS2-GFP system and microscopy approaches, we can visualize HIV-1 transcription sites with a good temporal resolution (1stack/3 seconds), during 15 minutes (ie : 3000 images), and with a sensitivity estimated to 5 polymerases per site. We observed that HIV-1 transcription, even in presence of Tat, occurs in pulses that are spaced by few minutes. We have developped theoritical and analytical tools to provide a quantitative description of HIV-1 transcription, and we are now able to extract several key information that are inaccessible otherwise.

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