FIGURE 6.

Both GN50 and GN300 extracts of HeLa cells contained stable complexes of ORC(1–6). A, FH-Orc1 was purified from a GN300 extract of 20 × 10⁷ cells by two-step affinity chromatography, and 100 μl was layered over a 3.7-ml 10–25% linear glycerol gradient in GN300. The gradient was centrifuged in a Beckman SW60 rotor for 4.5 h at 55,000 rpm (4 °C). B, FH-Orc2 was purified from a GN50 extract of 20 × 10⁷ cells and subjected to glycerol gradient centrifugation in GN50. C, FH-Orc6 was purified as in B.