The E4 Protein - A Late Starter
from: Papillomavirus Research: From Natural History To Vaccines and Beyond (Edited by: M. Saveria Campo). Caister Academic Press, U.K. (2006)
E4, expressed as a fusion protein (E1^E4), is the major protein expressed in papillomavirus (PV) infections. Its role in the PV life cycle is still unknown although emerging evidence suggests that it acts as a major regulator of the productive phase of the life cycle. However, an earlier role in the infectious cycle cannot be dismissed. E4 interacts with, and in some cases disrupts the organization of, a number of cytoplasmic and nuclear structures and organelles, including keratin intermediate filaments, the cornified cell envelope, mitochondria and ND10 domains. E4 can interfere with the normal progression of the cell cycle, and for some PV types this function seems to be regulated partly by posttranslational modification of the E4 protein. Few cellular partners of E4 have been identified, but one of these interactors is a cellular factor involved in mRNA metabolism. Thus, E4 is likely to have a pleiotropic role in the PV life cycle. To date, E4 functions suggest a role in facilitating and supporting viral genome amplification, the regulation of late gene expression, control of virus maturation and mediation of virus release read more ...