Figure 1.

Newly assembled spliceosomal snRNPs associate rapidly with CBs and IGCs (B-snurposomes). Differential interference contrast (DIC) and corresponding fluorescent micrographs of nuclear spreads from oocytes injected with fluorescent U1 or U7 snRNAs, respectively (green). Organelles are readily distinguished by their morphology with DIC and specific probes. Here, the DNA-specific dye Syto61 was used to labeled nucleoli (red), whereas the anticoilin antibody (mAb H1) was used to label CBs (blue; arrows). Newly made fluorescent U1 snRNP is detected in both CBs and IGCs (asterisks) as early as 1 h after cytoplasmic injection of fluorescent U1 snRNA. In contrast, a newly assembled fluorescent U7 snRNP, which is not involved in splicing, accumulates exclusively within CBs. In both cases, nucleoli are negative. Bars, 5 μm.