The E5 transforming gene of bovine papillomavirus encodes a small, hydrophobic polypeptide.

Bovine papillomavirus (BPV-1) contains two independent transforming genes that have been mapped to the E5 and E6 open reading frames (ORF's). The E5 transforming protein was identified by means of an antiserum against a synthetic peptide corresponding to the 20 COOH-terminal amino acids of the E5 ORF. The E5 polypeptide is the smallest viral transforming protein yet characterized; it had an apparent size of 7 kilodaltons. The transforming polypeptide is encoded entirely within the second half of the E5 ORF and its predicted amino acid composition is very unusual; 68% of the amino acids are strongly hydrophobic and 34% are leucine. Cell fractionation studies localized this polypeptide predominantly to cellular membranes.