"Internal Memo: The Structure of the Solenoid"

Date:: [c. 1976]

Reference:: PP/CRI/H/6/5

Catalogue details

Licence: In copyright

Credit: "Internal Memo: The Structure of the Solenoid". Source: Wellcome Collection.

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Internal Memo The Structure of the Solenoid Let us assume that solenoids exist, that their structure is fairly regular and, for simplicity, that solenoids are not bent to any great extent. Can we say anything useful about their structure? The main problem is that while the 140 bp core particle appears similar throughout nature the 'repeat' can vary somewhat, though the exact range of variation within one animal is unclear. Perhaps 180 to 210 bp may be the limits in vertebrates though the fungi appear shorter and sea urchins longer. Now we know that something like solenoids can be formed from monosomes; that is, with no connecting DNA. Thus they must form either by protein-protein interaction or by protein- DNA interaction Cor both). This suggests that the nucleosomes pack in a regular way. To understand what this means consider the dyad which passes through the centre of each nucleosome. Then by 'regular' we imply that these dyads are systematically arranged and in particular that each dyad is likely to be per pendicular to the axis of the solenoid and passing through it Cthe axis of the solenoid being presumed to be a straight line). All these assumptions lead to two questions: 1, How many 'turns' are there per repeat? Strictly by turns we mean the partial linking number of the equivdent straight ribbon. If the solenoid were practically flat