Immunocytochemical localization of nucleophosmin and RH-II/Gu protein in nucleoli of HeLa cells after treatment with actinomycin D.

HeLa cells were studied with the use of light microscopical immunocytochemistry to obtain more information on the nucleolar localization of nucleophosmin (B23 protein) and RH-II/Gu protein. In control cells these proteins are colocalized. After structural rearrangement of nucleoli induced by actinomycin D, nucleophosmin was present in the nucleolar periphery and nucleolar peripheral caps. In contrast, RH-II/Gu protein was observed mainly in central regions of nucleoli as a compact body. However, in some nucleoli the proteins colocalized in a small portion of the peripheral nucleolar cap. The proteins were also colocalized in micronucleoli but occasionally RH-II/Gu protein was absent or both proteins were not present.