Fig. 5. Further analysis of MHC-PML association. (A-D) Immuno-FISH was used to examine the MHC-PML association in untreated control fibroblasts (A) and compared with the association found in fibroblasts after treatment with interferon- (B), -amanitin (C) and DRB (D). PML bodies were detected by immunofluorescence (green) and the MHC region was visualised simultaneously using genomic probes recognising the LMP/TAP region (red). Note in C and D the clustering of PML bodies observed in a percentage of cells after transcriptional inhibition. (E-F) The MHC-PML association was also examined in fibroblast nuclei during G₁ phase (E) and S phase (F) of the cell cycle, detecting PML bodies (blue) and BrdU (green) by immunofluorescence, and visualising the MHC region by FISH using genomic probes recognising the LMP/TAP region (red). Projections of optical sections through each nucleus are shown.