Does anyone know which direction the nucleosomes are wrapped? I wonder:

  1. Relative to the B-DNA double helix twist direction (right-hand)
  2. Relative to the neighbor nucleosomes. Do they alternate to prevent supercoiling?

B-form DNA is wrapped around histones in a left-handed manner resulting in a left-handed solenoidal superhelix (see that, that and this). The reason for this wrapping is that it reduces the helical tension. This post has more information about DNA helical tension. Also note that exceptions exist (i.e. right-ended direction) especially for histone at the centromere as described in this paper.

For your second question, the exact way nucleosomes are then arranged to produce the chromatin fiber is, as far as I know, still not fully understood but the most accepted model is a zigzag arrangement (Woodcock CL & Ghosh RP, 2010 and Grigoryev SA & Woodcock CL).

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