ROLE OF MOUSE POLYOMAVIRUS LATE REGION IN THE CONTROL OF VIRAL-DNA REPLICATION - A REVIEW

The genome of polyomaviruses is divided into two coding regions: the e arly and the late region. A relatively short regulatory sequence, enco mpassing the origin of viral DNA replication (ori), separates the two regions encoding the structural genes. In mouse polyomavirus (Py) in p articular, the early DNA codes for three antigens: large, middle and s mall T-antigen (L-T, M-T and S-T, respectively). Large T antigen binds ori and thus regulates both viral DNA transcription and replication. Middle T antigen has been shown to mediate malignant transformation in non-permissive cells in vitro. No defined function has been assigned to the small T antigen although this gene product is thought to act sy nergistically both with L- and M-T antigens. The viral late region of Py encodes also three different genes whose products form the viral ca psid during the productive infection cycle in permissive cells. Py ear ly region was thought to be the only part of the genome necessary to c ode for proteins of functional and regulatory significance. The viral late region, on the other hand, was for a long time considered a simpl e reservoir of structural information, since it codes for capsid prote ins and was supposedly devoid of functional control properties. This s hort review is focused on recent works from our and other laboratories , reporting evidence that in Py also the late region has a functional role since late sequences are involved in the control of viral DNA rep lication and in capsid assembly. Results indicating that this might be true for the cognate simian virus SV40 will be also reviewed.