The intracellular expression pattern of the human papillomavirus type 11 E1--E4 protein correlates with its ability to self associate.

The function of the human papillomavirus type 11 (HPV 11) E1--E4 spliced protein is not known. E1--E4 protein in HPV-infected tissue is detected in the cytoplasm of differentiated epithelial cells and as immunoreactive bands corresponding to potential monomers, dimers and trimers in immunoblots. The yeast two-hybrid system was employed to test for self association of the HPV 11 E1--E4 protein. To confirm the results of the yeast two-hybrid experiments, coimmunofluorescence studies of a green fluorescent fusion protein (GFP-E1--E4) and a T7 epitope-tagged E1--E4 protein were performed in C33a keratinocytes. E1--E4 protein was shown to self associate in the yeast two-hybrid system, and this result was confirmed by colocalization of GFP-E1--E4 and T7-E1(wedge)E4 proteins in keratinocytes. Analysis of E1--E4 mutants established that the C-terminus was required for self association and that sequences in the N-terminus influenced the intracellular localization of E1--E4 protein. The intracellular expression patterns of GFP-E1--E4 and GFP-E1--E4 mutants were correlated with E1--E4 binding in the yeast two-hybrid system. Those E1--E4 mutants that did not self associate in the yeast two-hybrid system were detected as diffuse cellular fluorescence when expressed as GFP fusions. In contrast, GFP-E1--E4 was detected as a perinuclear aggregate. All E1--E4 mutants capable of associating with E1--E4 in the yeast two-hybrid system were detected as aggregates when expressed as GFP fusion proteins in keratinocytes.