Berlin 2008 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 2: DNA and Chromatin
BP 2.2: Vortrag
Montag, 25. Februar 2008, 10:45–11:00, PC 203
Higher-order folding of chromatin and the Random Loop Model — •Manfred Bohn1, Dieter W. Heermann1, and Roel van Driel2 — 1Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 19, 69120 Heidelberg — 2Swammerdam Institute for Life Sciences, University of Amsterdam, Kruislaan 318, 1098 SM Amsterdam
Remarkably little is known about the higher-order folding motifs of the chromatin fiber inside the cell nucleus. Folding depends among others on local gene density and transcriptional activity and plays an important role in gene regulation. Strikingly, at fiber lengths above 5 to 10 Mb (mega base pairs) the measured mean square distance <R2> between any two points on the chromatin fiber is independent of genomic distance. The formation of loops on different length scales seems to play an important role in transcriptional regulation. We analyze the data with respect to different polymer models on short fiber lengths. For long fiber lengths above 10 Mb, where simple models fail in explaining experimental results, we propose a polymer model that explains the leveling off by means of random looping. An analytical expression is calculated for the mean square displacement over the thermal ensemble. The quenched average over the disorder of loops is performed numerically. A detailed investigation of this model shows that only a small number of loops on all scales are necessary to fit experimental data.