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. 2024 Jun 3;16(6):904. doi: 10.3390/v16060904

Figure 1.

Figure 1

HPV16 genome organization, protein functions, and viral life cycle during productive infection. (A) Genome organization of the HPV16 genotype. The HPV genome is a double-stranded DNA (indicated by the gray circle), with a size of about 7900 bp. The major six early (E) open reading frames (ORFs), namely E6, E7, E1, E2, E4, and E5, and the two late (L) ORFs, namely L1 and L2, are indicated by different colors, with E6 and E7 shown in dark pink. Furthermore, the HR HPVs express an additional early protein, E8ˆE2C, by spliced mRNA. The major early p97 and late p670 promoters are indicated by arrows. The early and late polyadenylation sites, pAE and pAL, respectively, are also indicated by grey bar lines. The long control region, LCR (alternatively named the upstream regulatory region, or URR), comprises the replication origin and sequences involved in transcription. (B) HPV16 proteins. List of the HPV16 proteins and their principal functions. (C) HPV life cycle during productive infection. The viral life cycle during productive HPV infection in the host epithelial tissue (schematically represented on the left) is characterized by a specific pattern of viral gene expression across the epithelial layers. The viral life cycle is strictly regulated and linked to the host cell epithelial differentiation process. As reported for the cervical epithelium, HPV gains access to the basal layer through the epithelial transition zones (TZ) of the uterine cervix, in the presence of microlesions, wounds, or cuts. After the infection of basal cells, the HPV genome is maintained in the nucleus in an episomal state at a relatively low copy number. The expression of E6 and E7, through the p97 promoter, is necessary to start the viral life cycle. As the infected cells migrate to the upper epithelial layers, the viral proteins E1, E2, E4, and E5 are upregulated via the p670 promoter to facilitate viral genome amplification. In the upper epithelial layers, the expression of the late viral capsid proteins, L1 and L2, promotes capsid assembly and subsequent release of the new virion from the epithelial surface. Text and figures are based on the following manuscript: [15,16,17,18,19]. Created with BioRender.com.