Fig. 1. Reduction in the amount of securin after UV irradiation in the S and G2 phases of the cell cycle occurs in both cytoplasm and nucleus. HeLa cells were synchronized in S and G2 phases, and exposed to UV radiation where indicated. C, synchronized and nonirradiated cells. (A) Immunofluorescence experiments using an immunoaffinity-purified polyclonal anti-securin antibody, a monoclonal anti-CCNB1 (cyclin B) antibody and DAPI. In the merge, securin staining is shown in green, cyclin B in red, and DAPI in blue. Original magnification x403. (B) Detection of securin in subcellular fractions from synchronized cells. Fractions were separated by SDS-PAGE, transferred, and probed with the indicated antibodies. Anti-Raf and anti-hnRNP C were used to control for purity of the fractions. CE, cytosolic extracts; NE, nuclear extracts.