Berlin 2015 – scientific programme
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BP: Fachverband Biologische Physik
BP 44: DNA/RNA and related enzymes
BP 44.2: Talk
Thursday, March 19, 2015, 15:30–15:45, H 1058
Mechanisms of backtrack recovery by RNA polymerases I and II — •Ana Lisica1, 2, Marcus Jahnel1, 2, Christoph Engel3, Edgar Roldan4,5, Patrick Cramer3, and Stephan Grill1, 2, 4 — 1BIOTEC, Dresden, Germany — 2MPI CBG, Dresden, Germany — 3MPI PBC, Göttingen, Germany — 4MPI PKS, Dresden, Germany — 5GISC, Madrid, Spain
RNA polymerases (Pol) backtrack frequently during transcription elongation. To recover from the backtracked state, Pol I uses a strong transcript cleavage activity, while that of Pol II is weak but can be enhanced by transcription factor TFIIS. However, backtrack recovery can also proceed by 1D diffusion, and the mechanisms that underlie the choice of backtrack recovery pathway have not been investigated. Here, we use dual-trap optical tweezers to compare Pol I and Pol II transcription and backtrack dynamics. We find that Pol I is faster than Pol II, pauses less often, and can transcribe against higher opposing forces. Neither enzyme can recover alone from backtracks beyond a threshold depth, and only Pol II with TFIIS can rapidly recover from deep backtracks. Comparing recovery times from varying backtrack depths with expectations from the theory shows that the choice of backtrack recovery pathway is determined by a kinetic competition between 1D diffusion and transcript cleavage. In Pol I, this balance is influenced by the TFIIS-homologous subunit A12.2, which both decreases the rate of 1D diffusion and increases the rate of cleavage. Our data identifies the distinct backtrack recovery behaviours of Pol I and Pol II that evolved to serve specific cellular roles of these enzymes.