REVERSIBLE NUCLEOLAR TRANSLOCATION OF EPSTEIN-BARR VIRUS-ENCODED EBNA-5 AND HSP70 PROTEINS AFTER EXPOSURE TO HEAT-SHOCK OR CELL-DENSITY CONGESTION

The Epstein-Barr virus (EBV)-encoded, nuclear matrix-associated EBNA-5 protein is preferentially localized within distinct nuclear blobs in EBV-immortalized lymphoblastoid cell lines. We have previously found t hat the same blobs also contain retinoblastoma (Rb) protein. We now sh ow that they contain hsp70 protein as well. Both EBNA-5 and hsp70 tran slocate to the nucleolus under cell density congestion or after heat s hock. Both proteins relocate to their original position upon the reest ablishment of normal physiological conditions. EBNA-5 is tightly bound to the nuclear matrix. The translocated EBNA-5 is also tightly associ ated with matrix structures, as shown by sequential elution-based cell fractionation. The Rb protein does not translocate to the nucleolus. The virally encoded EBNA-1, -2, -3 and -6, and cellular PCNA, snRNP an d cyclin E are not affected either. The translocation of EBNA-5 to the nucleolus is not species- or cell type-specific since stress conditio ns induced the same phenomenon in EBNA-5-transfected human, mouse and rat cells of different tissue origins.