Table 1 Characteristics of functional early and late structural HPV genes.

E1

Ori-binding DNA helicase required for replication and amplification of the virus.

[101]

E2

Master regulator of the viral life cycle

Initiating the replication process and partitioning of the viral genome.

Functioning as a transcriptional activator or repressor.

Participating in virus genome segregation over host cell mitosis process.

[23, 102, 103]

E1^E4

Being expressed at the late stage of viral infection to facilitate the virus leaving the host cell by disrupting the host cytokeratin network.

[104,105,106,107]

E5

Oncogenic small hydrophobic transmembrane proteins playing a role in the productive virus life cycle.

[44]

E6

Oncogenic protein inhibiting p53 protein via a direct physical interaction.

Preparing cellular environment to allow for replication and immortalisation.

[28]

E7

Oncogenic protein inhibiting Rb protein via a direct physical interaction.

Preparing cellular environment to allow for replication and immortalisation.

[29]

E8^E2

Inhibiting viral replication and gene expression.

[108]

L1

Being expressed upon cellular differentiation.

Main structural component of the viral capsid.

[109]

L2

Expressed upon cellular differentiation.

Minor capsid protein playing an active role in the assembly of HPV virus throughout the infectious process.

[110]