Index >>Viruses and Cancer >>Polyoma and SV40 Viruses

A double stranded break of the super coiled form converts it into the linear form (form III) with a sedimentation coefficient of l4S. In the polyoma virus the G+C content is 47-50 per cent, while in SV40 it is 41 per cent.
The polyoma virus is responsible for tumours in mice, The virus can be cultured in permissive mouse cell lines, the cells of support replication and growth of the virus.
The virus undergoes lytic cycle in which the host cells ultimately die and liberate a large number of virus particles The virus can also infect rat and hamster cells, which are transformed into tumour cells without liberating large amounts of virus particles.
Such infection is said to be non lytic, and the cells are called non permissive cells.

The T antigen was found in the cells after 4-5 hours. After the appearance of the T antigen several DNA metabolism enzymes begin to increase in concentration in infected cells.
These include DNA polymerase, DNA ligase and thymidine kinase.
They appear to be coded by the host cell, as the viral genome is insufficient for coding them.
Late proteins : The capsid (structural) proteins are the late proteins. In SV 40 only two capsid proteins have been identified.
These are the major capsid protein VPI (MW 45,000) and the minor capsid protein VP2 (MW 30,000). VP5 may be present, but the data are not consistent.
The polyoma viruses have the capsid proteins VP, VP2 and V 3. There are common sequences in VP2 and VP3, but no common s­equences between the major capsid protein VP1 and the minor capsid proteins VP2/VP3