Practice question

Quantitation of DNA trajectory around histone octamer shows slightly more than one and half circles. High resolution structures measure 1.65 to 1.67 superhelical turns protecting 147 base pairs, about 83 base pairs per full superhelical turn, creating fourteen histone-DNA contact points via arginine side chains inserted into minor grooves. One turn would protect only 80 base pairs, two full turns would need 166 base pairs which exceeds core length. Value 1.65 explains why linker DNA emerges close together, why H1 can bridge entry exit and sealing two turns, enabling higher order folding into 30 nanometer fiber.