A rabbit antiserum has been prepared using as antigen the 110,000-dalton mammalian heat-shock protein. This protein was purified for injection by two-dimensional PAGE of heat-shocked Chinese hamster ovary cells. Characterization by immunoautoradiography and immunoprecipitation reveals that the antiserum is specific for the 110,000-dalton protein.Both techniques also reveal that the protein against which the antiserum is directed is induced by heat shock. Indirect immunofluorescence shows that the antigen is primarily localized at or near the nucleolus in cultured cells and numerous murine tissues. Treatment of cultured cells with deoxyribonuclease destroys the organization of staining within the nucleus while ribonuclease appears to completely release the antigen from the nucleus. A binding of the antiserum to cytoplasmic structures is also observed by immunofluorescence. This association with nucleoli may have implications in the regulatory aspects of the heat-shock response.A hyperthermic challenge to a cell can result in a reorganization at translational and transcriptional levels (7, 23) and at the same time protect the cell from additional applications of the same stress (8), probably through the intervention of heatshock proteins (14,15,17,18,27,28). Despite the implications of this, it is important to recognize that the function of heat-shock proteins remains a mystery. However, reports indicate that at least some heat-shock proteins my localize in the nucleus (2,3,13,16,31,32), suggesting a direct role in the regulatory changes associated with this response.To learn more regarding the function of heat-shock proteins and their role in regulation and protection, we investigated mammalian heat-shock proteins using an immunologic approach. We report here on the characterization of an antiserum against the major l l0,000-dalton mammalian heatshock protein (HSP 110). ~ It is demonstrated by indirect immunofluorescence that this protein is localized at or near the nucleolus and is released from the nucleus by treatment with ribonuclease. This suggests that aspects of nucleolar function may be important in the protective and regulatory properties of the heat-shock response. mented with 15% heat-inactivated newborn calf serum. In heat-shock experiments: flasks were immersed horizontally into a constant temperature water bath (Haake FK-2) for the indicated times at 45"C + 0.1°C. 10TY2 mouse embryo fibroblasts were originally obtained from Dr. John Bertram of this Institute. These cells are grown in Eagles basal medium with Earle's salts (Gibco Laboratories) supplemented with 10% heat-inactivated fetal calf serum. Frozen sections were obtained from tissues of BALB/c CR mice supplied by the West Seneca Laboratories of this Institute.
MATERIALS AND METHODS
Cells
Preparation of Antigen and Immunoautoradiography:Heat-shock proteins were identified by autoradiography of two-dimensional O'Farrel gels, as previously modified and described (10,19), by applying a [35S]methionine pulse during the peak induction peri...