Zig-zag model of 30 nm fiber is favored by:
Recent cryo-electron microscopy favors two-start zigzag model where nucleosomes form two interleaved stacks connected by relatively straight linkers crossing interior. This arrangement stabilized by linker histone H1 bridging adjacent nucleosomes and promoting face to face stacking via H4 tail acidic patch interaction. Low H1 fails to align zigzag, leaving extended array with weak compaction. High H1 concentration plus divalent cations favors zigzag tetranucleosome as fundamental repeat. Therefore zigzag model similarly requires H1 but explains why linker DNA remains straight rather than bent
Ref: Song et al., Science 2014 Cryo-EM Structure; Dorigo et al., 2004: Zig-zag Model Favored with High H1
