Methods
coimmunoprecipitation and flow cytometry-based FRET assays. Analytical ultracentrifugation of the recombinant proteins revealed that the stoichiometry of the E6/E7 complex involves two E7 molecules and two E6 molecules. In addition, fluorescence polarization showed that (I) E6 binds to E7 with a similar affinity for HPV16 and HPV31 (in the same micromolar range) and (II) that the binding interface involves the unstructured N-terminal region of E7. The direct interaction of these highly conserved papillomaviral oncoproteins may provide a new perspective for studying HPV-associated carcinogenesis and the overall viral life cycle.