Schematic representation of HPV oncoproteins E5, E6 and E7. HPV16-E5 is an 83-amino acid-long transmembrane protein with three transmembrane domains (TMDI-III). HPV-16 E6 is an 158 amino acid protein with two CXXC (Cys-X-X-Cys,) motifs, which participate in coordinating with zinc ions and are indicated in the schematic. The C-terminus PDZ-binding motif (PBM) sequence ‘ETQV’ is shown, which can be phosphorylated by AKT, Chk2 via PKA and Chk1 kinases. HPV-16 E7 is a cytoplasmic phosphoprotein. The position of the conserved regions (CR1, CR2 and CR3) and CXXC (Cys-X-X-Cys) motifs, which participate in coordinating zinc ions, are also indicated. The LXCXE motif and CKII phosphorylation site in the CR2 region are important for targeting the pRB and related pocket proteins.