THE HUMAN PAPILLOMAVIRUS TYPE-16 E7 PROTEIN IS ASSOCIATED WITH THE NUCLEOLUS IN MAMMALIAN AND YEAST-CELLS

In this study we show, by immunofluorescence and electron microscopy i mmune-gold labelling, that the major transforming protein of Human Pap illomavirus type 16 E7 is associated with the nucleolus of cells deriv ed from the HPV16-positive cervical carcinoma line CaSki. The E7 nucle olar staining appeared to be cell cycle dependent, being considerably reduced in the G(2) phase. The total level of the protein in the cell, however, remained constant during all phases, We also show that the c ellular protein Rb1, which is targeted by E7, is localised in the nucl eus and nucleolus in CaSki cells. Thus, it is possible that the presen ce of E7 in the nucleolus correlates with a hypothetical function(s) o f Rb1 in this particular intranuclear compartment. The nucleolar local isation of HPV16 E7 protein was also observed in the fission yeast Sch izosaccharomyces pombe, suggesting that a targeting mechanism of HPV16 E7 protein into the nucleolus is common to both mammalian and yeast s ystems, Nucleolar localisation of HPV16 E7 protein may be independent from Rb1 since no Rb1 related proteins have been identified in fission yeast.