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DNA in human and stallion spermatozoa forms local hexagonal packing with twist and many defects
N Sartori Blanc1, A Senn, A Leforestier
1Laboratoire d'Analyse ultrastructurale, Université de Lausanne, Bâtiment Biologie, Lausanne, CH-1015, Switzerland.
Abstract:
In human and other mammal sperm nuclei, DNA is packed in a highly condensed state, the structure of which remains unsolved. Cryoelectron microscopy of vitrified sections provides a first direct view of the local arrangement of the nucleoprotamine filament. DNA aligns in parallel in layers and its orientation rotates along a single-twist direction as in a cholesteric liquid crystal. The structure contains numerous defects, which introduce locally double-twist configurations. Destruction of the SS bonds with dithiotrehitol relaxes the twist and favors the extension of the hexagonal close packing of the filaments, though keeping constant their interfilament distance.