Berlin 2012 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 24: Posters: DNA/RNA and Related Enzymes

BP 24.7: Poster

Donnerstag, 29. März 2012, 17:30–19:30, Poster A

Imaging of DNA overwinding and splitting — •Hua Liang, Nikolai Severin, and Jürgen Rabe — Department of Physics, Humboldt University Berlin, Newtonstr. 15, D-12489 Berlin, Germany

Unwinding and melting a DNA double helical structure at a specific region is the initiation step for DNA replication, the precise mechanism of which remaining still ambiguous (1). Experimental and theoretical studies on stretching and twisting of double-stranded (ds-) DNA reveal its chirality by mechanical twist-stretch coupling: small stretching along the DNA backbone induced torsional stress along the molecular backbone and vice versa (2). It has been theoretically shown that ds-DNA may release its torsional stress inhomogeneously along the backbone with localized, sequence-dependent structural failure to preserve its B-form, when supercoiling is not allowed (3). However, the pulling experiments were carried out in solution, where it is difficult to access the direct conformational changes during stretching. Here we report the experimental observation of plasmid DNA (pUC19 and pBR 322) overwinding with local splitting of the double helix into two single strands when stretched on a surface. Only one split is observed for different lengths of DNA, with the splitting length proportional to the total length. We discuss a possible unwinding and splitting mechanism analogue to many biological processes which involve DNA in vivo such as replication, transcription initiation, and DNA repair. [1]M. L. Mott, J. M. Berger, Nature Reviews Microbiology 5, 343 (2007. [2]J. Gore et al., Nature 442, 836 (2006). [3]G. L. Randall, L. Zechiedrich, B. M. Pettitt, Nucleic Acids Research 37, 5568 (2009).