Localization of the 70 000 dalton heat-induced protein in the nuclear matrix of BHK cells.

The exposure of exponentially growing BHK cells to supranormal temperatures (41-44 degrees C, for 15 min to 1 h) induces the synthesis of a new set of proteins, the heat shock proteins, while the synthesis of proteins made before heat shock is repressed at 43 degrees C. Among the two major heat shock proteins induced, of molecular weight 70 K and 68 K, only the 70 kD protein is found bound to the nuclear matrix. This protein is resolved differently from the normal matrix proteins by isoelectric focusing and, when blotted, does not react with antibodies directed against nuclear matrices. These results show that the 70 kD heat shock protein is a new protein transferred from the cytoplasm to the nucleus, where it binds to the nuclear matrix, suggesting a structural role for this protein.