FIG. 2.

Structure-based analysis of the putative zinc-binding domains of avian PV E6 and E7 ORFs. (A) General folding of an E6 zinc-binding domain (here, HPV-16 E6C) (23). Secondary-structure elements are indicated. Arrows indicate proposed locations for inserted sequences within avian PV E6. C-ter, C terminus; N-ter, N terminus. (B) General folding of an E7 zinc-binding dimeric domain (here, HPV-45 E7C) (25), with the secondary-structure elements indicated. (C) Alignment of the full FlPV-1 and FPV E6 ORFs with HPV E6 zinc-binding domains HPV-16 E6C and HPV-16 E6N, in the context of structural information derived from the published structure of HPV-16 E6C (23). Plotted above the alignment is the percentage of accessibility to the solvent for each structured residue within the published structure of HPV-16 E6C (23), calculated as described by Chothia (4) and using the WHATIF program (40). Arrows and cylinders denote beta-strands and α-helices, respectively. Positions playing a key structural role within the HPV-16 E6C structure are colored as follows: magenta, hydrophobic (W, F, Y, L, I, V, M); green, basic (K, R, H); red, acidic (E, D); orange, polar (Q, N, T, S); brown, cysteine (C); and cyan, small (G, A, P). Boxed, boldfaced characters pointed out by arrowheads indicate presumably exposed hydrophobic positions of FPV E6 substituted by hydrophilic positions in FlPV-1 E6. (D) Alignment of the zinc-binding C-terminal domains of FlPV-1 FPV and PePV E7 ORFs with the equivalent domains in HPV, for which structural data are available, as follows: HPV-1a E7 (18) and HPV-45 E7 (25). Structural information is derived from the HPV-45 E7 structure.