Table 1.

Summary of the experimentally measured tether shortening, the estimated number of nucleosomes, the corresponding degree of completion of assembly, and the superhelical density that blocks nucleosome formation

Experiment number	Tether shortening (μm)∗	Estimated number of nucleosomes formed†	Completion (%)‡	Positive superhelical density σ that blocks nucleosome formation§
Partial assembly
1	1.9	38	39	0.036
2	2.3	46	47	0.049
3	1.6	32	33	0.028
4	1.45	29	30	0.025
5	2.37	47	48	0.051
6	2.27	45	46	0.047
7	1.6	32	33	0.028
Average	1.93 ± 0.15	39 ± 3	39 ± 3	0.038 ± 0.004
Full assembly on nicked DNA
1	3.52	70	72
2	4.48	90	91
3	3.21	64	66
4	3.90	78	80
5	3.85	77	79
Average	3.79 ± 0.21	76 ± 4	77 ± 4
Full assembly with magnets rotation
1	3.5	70	71
2	4.39	88	90
Average	3.94 ± 0.44	79 ± 9	81 ± 9

^∗Maximal length of the tether is 16,500 bp, which corresponds to ∼5.6 μm (0.34 nm/bp). The maximum length measured experimentally was ∼4.6 μm. The slight difference between the expected and the measured length is due to the low stretching force applied (at low forces, the tether is not maximally extended).

^†Estimated number of nucleosomes formed is calculated based on the measured shortening and the expected change of DNA tether per nucleosome formed; 147 bp corresponds to ∼50 nm of naked DNA. Taking into account a range of possible nucleosome repeat lengths 146–200 bp, the 16,500 bp can accommodate between 83 and 113 nucleosomes.

^‡We took the average value (98) as the base for estimating the % of completion (number of nucleosomes formed/98).

^§Superhelical density σ that blocks nucleosome formation is estimated from the number of nucleosomes formed divided by total linking number of the remaining DNA tether (16,500—No. of nucleosomes × 147)/10.4. Values are reported ± SE.