Fig. 3.
Epigenetic regulation of the HPV transcription during the virus life cycle. Binding of nucleosomes to the HPV URR (contains the enhancer, origin of replication (Ori) and proximal promoter PE), epigenetic modifications (DNA methylation (CpG Me), histone methylation (Me) and histone acetylation (Ac)) and some of the major host epigenetic modifiers involved are shown in undifferentiated (a) and differentiated keratinocytes (b). Details are given in the text. Strongly bound nucleosomes are shown in dark blue, weakly bound in faint blue, and nucleosomes that are lost or repositioned upon differentiation are shown in faint blue and with dotted lines. Question marks (?) indicate uncertainty of the epigenetic modification occurring in differentiated cells. Plus and minus signs indicate stimulation or repression of viral transcription. Host factors known to bind the URR that are relevant to this review are shown only, alongside E1 and E2 binding