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. 1981 Mar;78(3):1461-5.
doi: 10.1073/pnas.78.3.1461.

Structure of chromatin and the linking number of DNA

A Worcel, S Strogatz, D Riley

Structure of chromatin and the linking number of DNA

A Worcel et al. Proc Natl Acad Sci U S A. 1981 Mar.

Abstract

Recent observations suggest that the basic supranucleosomal structure of chromatin is a zigzag helical ribbon with a repeat unit made of two nucleosomes connected by a relaxed spacer DNA. A remarkable feature of one particular ribbon is that it solves the apparent paradox between the number of DNA turns per nucleosome and the total linking number of a nucleosome-containing closed circular DNA molecule. We show here that the repeat unit of the proposed structure, which contains two nucleosomes with -1 3/4 DNA turns per nucleosome and one spacer crossover per repeat, contributes -2 to the linking number of closed circular DNA. Space-filling models show that the cylindrical 250-A chromatin fiber can be generated by twisting the ribbon.

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