Pulling chromatin apart: Unstacking or Unwrapping?

BACKGROUND: Understanding the mechanical properties of chromatin is an essential step towards deciphering the physical rules of gene regulation. In the past ten years, many single molecule experiments have been carried out, and high resolution measurements of the chromatin fiber stiffness are now available. Simulations have been used in order to link those measurements with structural cues, but so far no clear agreement among different groups has been reached. RESULTS: We revisit here some of the most precise experimental results obtained with carefully reconstituted fibers. CONCLUSIONS: We show that the mechanical properties of the chromatin fiber can be quantitatively accounted for by the stiffness of the DNA molecule and the 3D structure of the chromatin fiber.