Genome organization of HPV. Location of the HPV major proteins. The HPV genome encodes early proteins with regulatory (E1 and E2) and transforming (E6 and E7) functions and two late capsid proteins (L1 and L2). Protein E4 has a largely unknown function and E5 is a hydrophobic protein that enhances cell immortalization. Adapted from Faridi R, Zahra A, Khan K, Idrees M. Virol J. 2011; 8:269.