DNA-binding activity of papillomavirus proteins

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Abstract
We demonstrate DNA binding by papillomavirus (PV) open reading frame (ORF) proteins that correspond to the early transforming and trans-activating (E6 and E2) and late structural regions (L2 and L1) from bovine PV type 1 and human PV types 6b and 16. All PV proteins were synthesized in Escherichia coli and had a common 13-amino-acid leader sequence from the expression vector pRA10. Antibodies have been generated in rabbits against these PV proteins. The pV ORF proteins bind double-stranded DNA, and this activity is demonstrated to be inherent to the PV proteins. DNA-binding activity by PV proteins is optimal at 50 mM NaCl and at pH 7.0. For some PV proteins (e.g., bovine PV type 1 E2), DNA binding is enhanced at a lower pH (pH 6.0) and NaCl concentration (50 to 100 mM). DNA binding is inhibited by the appropriate antibodies. The possible significance of these findings is discussed in relation to the genetic and structural evidence on the function of these ORFs.