Analysis of HPV‐1 E4 gene expression using epitope‐defined antibodies.

Six monoclonal antibodies (mAbs) have been raised against the E4 proteins of HPV‐1. Five of these were found to recognize denaturation‐resistant epitopes as determined by Western blotting–and their binding sites were identified by determining their reactivity against a panel of bacterial E4–beta‐galactosidase fusion proteins which contained progressive deletions at the C‐terminal end of the E4 region. The five mAbs were found to bind to four distinct sites. By using these epitope‐defined mAbs, along with anti‐peptide antibodies raised against putative N‐ and C‐terminal E4 sequences, we have determined the relationships between the eight distinct polypeptides (mol. wt 10/11 kd, 16/17 kd, 21/23 kd and 32/34 kd) previously shown to be expressed from the E4 gene of HPV‐1 in productively infected papillomas. The 17 kd E4 polypeptide appears to be the product of a spliced mRNA encoding five amino acids from open reading frame (ORF) E1 joined onto 120 from the E4 ORF. The 16 kd and 10/11 kd proteins, which may be derived from this, lack sequences (approximately 15 and 70 amino acids respectively) encoded by the 5′ end of the E4 gene. The 32/34 kd proteins were detected by all antibodies which reacted with the 16/17 kd polypeptides, suggesting that they represent dimers of the latter species. The 21/23 kd polypeptides, however, do not appear to be simple dimers of the 10/11 kd protein as previously predicted, and reacted with antibodies whose epitopes mapped in the N‐terminal half of the E4 protein.(ABSTRACT TRUNCATED AT 250 WORDS)