() Nuclear localization: Psc1-HA transfected COS-1 cell (i) visualized with anti-HA FITC antibody (ii) and anti-SC35 antibody (iii). (iv), Merged image of (ii) and (iii). Left arrow indicates Psc1 nuclear speckles that do not contain SC35 and tend to be associated with the nuclear periphery, right arrow indicates Psc1 and SC35 colocalization in yellow. (v), merged image of panels (i) and (iv). The arrow shows the proximity to the nuclear membrane of Psc1-containing nuclear speckles that do not contain SC35. () Cytoplasmic localization: (i), Psc1-HA transfected COS-1 cell visualized with anti-HA FITC antibody showing cytoplasmic localization in the absence of nuclear localization. (ii), GFP–Psc1 transfected COS-1 cell showing nuclear and cytoplasmic localization. () Subcellular distribution of GFP–Psc1 within a population of GFP–Psc1 transfected COS-1 cells. Error bars indicate standard deviation. () COS-1 cells were co-transfected with Psc1-HA and GFP–SF2/ASF and visualized with anti-HA TRITC (lower right) or by direct fluorescence (lower left). The top panel shows merged images of the lower panels. () Specificity of purified polyclonal anti-Psc1 antibody raised against Psc1 amino acids 635–713. Western blot analysis of: lane 1, untransfected COS-1 cells (10) were lysed and the pellet fraction probed with purified anti-Psc1 antibody; lane 2, 5 μl of 50 μl unprimed rabbit reticulocyte lysate transcription/translation reaction probed with anti-FLAG monoclonal antibody; lane 3, 5 μl of 50 μl HisFlag primed rabbit reticulocyte lysate transcription/translation reaction probed with anti-FLAG monoclonal antibody. () Endogenous Psc1 in COS-1 cells. Untransfected COS-1 cells were visualized with anti-Psc1 antibody. Panels show endogenous Psc1 in nuclear speckles in the absence (i) or presence (ii) of cytoplasmic speckles. (iii) Merged image of COS-1 cell visualized with anti-SC35 (red, lower left panel), and anti-Psc1 (green, lower right panel). Arrows indicate endogenous Psc1-containing nuclear speckles that do not contain SC35. Nuclei were stained with 5 μg/ml Hoechst 33258 (lower panels i and ii). Size bars represent 10 μm. Fluorescence images in (A) were obtained using confocal microscopy. All other images were obtained by conventional microscopy.