Figure 3.

Characterization of the FITC–UTP foci. When FITC–UTP is co-injected with increasing concentrations of unconjugated UTP, the fluorescent signal is competed away. The photomicrographs represent 0 (a), 50 (b) and 100 (c) mM UTP added along with 1 mM FITC–UTP. HEp-2 cells were nuclearly microinjected with 1 μg/ml of α-amanitin, and after 10 min, the cells were microinjected with FITC–UTP and then processed for microscopic evaluation. Compared with untreated control cells (d), microinjection of α-amanitin (e) inhibits the FITC–UTP labeling of foci and diminishes incorporation into the nucleoplasm but not nucleoli. A corresponding image of PML labeling (f) demonstrates that the structural integrity of the PML body is not affected by α-amanitin. The effect of actinomycin D-mannitol on incorporation of FITC–UTP was examined in cells incubated for 1 h at concentrations of 0 (g), 0.01 (h), and 0.20 (i) μg/ml. Actinomycin D appears to inhibit pol I synthesis at the lower dose and pol I and pol II at the higher dose.