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. Author manuscript; available in PMC: 2008 Jan 1.
Published in final edited form as: Adv Pharmacol. 2008;56:509–557. doi: 10.1016/S1054-3589(07)56016-3

FIGURE 2.

FIGURE 2

The HPV life cycle. Virions enter the stratified epithelium through a site of wounding, where they gain access to the mitotically active basal-layer keratinocytes. During the maintenance phase, expression of E6, E7, and E5 induces cell proliferation, and the viral genome is replicated extrachromosomally at low-copy number (5-50 copies per cell). As the cells differentiate, the expression level of E1, E2, and E4 increases in the spinous layer. A transition from theta to rolling-circle replication results in an increase in copy number up to 100-1000 copies per cell. Postamplification, high levels of L1 and L2 capsid genes are expressed and capsid assembly occurs in the granular and squamous layers of the stratified epithelium. Progeny virus is released by desquamation.