= Solution
The naked labelled <DNA> runs fastest. Reconstitution creates a slower <nucleosome> band, with a little residual unassembled <DNA>. Adding NVNA1 progressively generates several additional, more slowly migrating labelled species and reduces the unbound <nucleosome> population. \b[These are consistent with <ternary protein–DNA complexes> containing <DNA>, <histones> and NVNA1, with increasing occupancy or altered assembly.] The naked-DNA titration also shows several NVNA1–DNA species, reflecting different occupancy states on the repeat-containing fragment.
A mobility shift reports changes in charge, size and shape together. It cannot by itself establish that <histones> remain in every shifted species, or identify exact <protein> stoichiometries. In particular, similarity to a band in the naked-DNA lanes could indicate <histone> loss rather than merely another occupancy state. The specific-competitor experiment in the next part supplies the important compositional test: removal of NVNA1 can regenerate a <nucleosome> band, demonstrating retention of <histones> in the starting ternary population.
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