Simian Virus 40 (SV40) is a non-enveloped DNA tumour virus that enters cells by caveolar endocytosis and is delivered to the endoplasmic reticulum (ER) in intact form. Some evidence suggests that from there it transported to the cytosol before entering the nucleus through nuclear pore complexes. Replication of the virus occurs in the nucleus. We are interested in why SV40 enters the endoplasmic reticulum (ER), (i.e. whether ER entry is essential to infection and if so why), how SV40 penetrates through the membrane of the ER, and how it is transported to the nucleus.