Figure 4.

Mus81 is retained in the nucleoli of actinomycin D– and α-amanitin–treated cells, but not in DNAse I–treated cells. HeLa cells were incubated with 50 ng/ml actinomycin D and/or 0.5 μg/ml α-amanitin for 1 h before harvest. After in situ extraction and fixation, samples were costained for WRN or Mus81, the nucleolar protein, nucleophosmin/B23, and for DNA. (A) Nucleolar WRN became predominately nuclearplasmic after treatment with actinomycin D. (B) The nucleolar staining of Mus81 was not affected by actinomycin D or α-amanitin treatment. (C) Digestion of DNA results in the loss of nucleolar Mus81 staining.