Capsid protein-encoding genes of hamster polyomavirus and properties of the viral capsid

On the basis of its genome organization the hamster polyomavirus (HaPV) is closely related to the murine polyomavirus Py. But HaPV infection, in contr ast to Py infection, gives rise to two different tumor types; depending on the hamster strain used for infection, HaPV induces either epitheliomas or lymphomas. Although the HaPV virions were shown to be similar to those of P y and SV40, more precise information about the structure and protein compos ition of the HaPV capsid was still missing. Here we describe the primary st ructure of the capsid protein-encoding HaPV genes and the structure and pro tein composition of the HaPV capsid, Virions isolated from epitheliomas in HaPV-infected hamsters were shown by electron microscopy to be spherical pa rticles with the typical icosahedral structure of polyomaviruses. However, in contrast to the capsids of SV40 and Py, a T = 7 laevo symmetry of HaPV c apsids was observed. Separation of HaPV virions in SDS polyacrylamide gels and Western blotting with VP1-specific antisera identified VP1 as the major capsid protein species corresponding in its molecular weight to the predic ted value of 41.8 kDa, Because of the presence of two potential translation al initiation sites in the VP1 gene, the N-terminal amino acid sequence of virion VP1 was determined and found to start at the second initiation site, The amino acid homologies of HaPV capsid proteins shared with Py varied be tween 65.5% (VP1), 45.4% (VP3) and 44.6% (VP2), whereas the homologies to t he relevant proteins of other polyomaviruses were found to range between 49 .6-57.9% for VP1 and 28.9-41% for VP2/VP3.