FIGURE 2.

Cell cycle dynamics of ORC assembly. A, flow cytometry profile of DNA content of double thymidine blocked and released HeLa suspension cells. Cell cycle profile of asynchronous and synchronized cells at the indicated hours after release are shown; x axis shows propidium iodide-area levels, and y axis shows cell count at different time points after release. B, expression levels of pre-RC proteins and cell cycle markers in synchronized HeLa nuclear extracts were studied by Western blot. Ponceau S-stained blots are shown as loading controls. C, immunoprecipitation of Orc1, Orc2, Orc3, or control IgG from double thymidine block and release synchronized HeLa S3 nuclear extracts. Co-immunoprecipitation of Orc1, Orc2, Orc3, and Orc4 were investigated by Western blots as indicated.