Fig. 1: The spatial distribution of ORC is dominated by the origin.

a From left to right: scheme of the flow cell, experimental workflow, and a representative image of labeled ORC bound to a single DNA molecule. The dashed square highlights the region used for data analysis. A DNA molecule is tethered to beads that are trapped in a dual-beam optical trap, allowing the DNA to be held under tension. When labeled ORC is introduced and binds to the DNA, it is excited by an integrated confocal laser scanning system (for further details, see Methods). b–e (i) Histograms of the spatial distribution of DNA-bound JF549-ORC following a 2 min-long incubation. (ii) Distribution of the stoichiometry of ORC foci everywhere on the DNA, and (iii) within 0.2 µm of the HtH origin (iii). Specific conditions are: b incubation of ORC in ATPγS; c ORC and Cdc6 in ATPγS; d ORC in ATP; e ORC and Cdc6 in ATP. f As in b, except that DNA contains the mHtH origin as described in Supplementary Fig. 7. g As in b, except that JF549-ORC is incubated with the 21.2 kbp DNA in bulk for 30 min before being introduced into the flow cell and imaged as in b–e. Bold dashed lines in the seventh bin from the left indicate the head-to-head (HtH) high-affinity ORC-binding sites. Faint dashed lines indicate near-cognate binding sites elsewhere on the DNA.