Fig. 6. Replication initiates with a significant degree of specificity within permeabilized CHO post-ODP nuclei incubated in licensing-deficient Xenopus egg extracts. Digitonin-permeabilized pre-ODP (2 hours in G1; triangles and hatched circles) or post-ODP (6 hours in G1; diamonds and circles) nuclei were incubated in control untreated (diamonds and triangles) or geminin-supplemented (filled circles and hatched circles) Xenopus egg extracts and the specificity of initiation within the DHFR locus was measured by the ELFH assay. Squares represent intact post-ODP nuclei incubated in control untreated egg extracts. Similar results were obtained in three independent experiments. The relative specificity of initiation at ori-ß within permeabilized post-ODP nuclei (measured as the average specificity of probes C, D, E and R, mapping to the region of peak initiation activity) varied in different experiments between 25 to 60-70% of that within intact post-ODP nuclei.