Human papillomavirus type 16 E7 protein expressed in Escherichia coli and monkey COS-1 cells: immunofluorescence detection of the nuclear E7 protein.

Human papillomavirus type 16 E7 protein, expressed in Escherichia coli as fusion protein lac alpha peptide-E7 (lac-E7), was purified by electrophoresis and used to immunize rabbits to raise antisera. The anti-lac-E7 sera recognized another bacterially expressed fusion protein trpE-E7 by the Western blot method. The antisera were used to identify E7 protein transiently expressed in monkey COS-1 cells from an SV40-derived expression plasmid containing E7 gene. Like the E7 protein from CaSki cells, the majority of 19K E7 protein in the transfected COS-1 cells was found by immunoprecipitation in the soluble cytoplasmic fraction. By immunofluorescence staining, however, the E7 protein was detectable in the nuclei of the transfected COS-1 cells. The results suggest that the E7 protein expressed in monkey cells is nuclear, although it is readily released from nuclei when the cell structure is broken.