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BP: Fachverband Biologische Physik

BP 33: Biological Machines \& Motor Proteins

BP 33.1: Hauptvortrag

Freitag, 18. März 2011, 10:15–10:45, ZEU 250

Clamping DNA Strands Together: The Mechanics of Single-strand Annealing — •Erik Schäffer and Marcel Ander — Biotechnology Center (BIOTEC), TU Dresden, Dresden, Germany

Homologous recombination is the fundamental biological process for exchanging DNA segments. It serves to repair DNA breaks, re-launch stalled replication forks, and maintains genetic diversity by mediating gene transfer mechanisms. Two mechanisms are known: strand invasion and single-strand annealing. While the former ATP-dependent mechanism promoted by RecA/Rad51 has been characterized to some extent, the latter ATP-independent mechanism is not understood on the molecular level. Using optical tweezers, we investigated the single-strand annealing mechanism using Redß as a model system. We discovered that despite Redß's efficiency in promoting single-strand annealing, it defaults to kinetic inhibition of DNA annealing. Instead, it is active towards the 3'-end of a single-stranded DNA in the following way: If sufficient complementarity towards another single-stranded DNA is given, presumably a monomer of Redß nucleates clamping of DNA strands. The clamping leads to a large energetic gain and resistance against DNA unzipping. Sequence conservation patterns suggest the existence of three distinct superfamilies: Redß, ERF, and Rad52. For the human version of the latter, we have also indications for the clamping mechanism suggesting that it is perhaps the underlying general mechanism of DNA single-strand annealing, irrespective of the protein family.