FIG. 1.

Diagram of HPV31 genome showing viral open reading frames (ORF) with early and late promoters and polyadenylation sites. The E4 ORF and the overlapping E2 ORF are shown as open boxes. The N-terminal amino acid sequences of wild-type E1^∧E4 as well as of the E4M4 and E4M9 mutant forms are indicated at the bottom of the diagram. For E4M4, a translation termination codon was inserted after the first four amino acids of the E4 ORF, while for E4M9, a stop codon was inserted after nine amino acids. The E4M4 mutation introduced a change in the E2 coding sequence from a serine to a threonine, while the E4M9 mutation was silent in E2. The E1^∧E4 protein consists of the first five amino acids of E1 fused to the E4 open reading frame (bold letters).