Identification and characterization of the hamster polyomavirus middle T antigen

The study identified and characterized the hamster polyomavirus (HaPV) middle T antigen (HamT) as a 45-kDa protein associated with lymphoid and hair follicle tumors in Syrian hamsters. HamT was found to be similar to the mouse polyomavirus middle T antigen in its association with serine/threonine phosphatase, phosphatidylinositol-3 kinase, and protein tyrosine kinase activities. However, unlike the mouse middle T antigen, which predominantly associates with pp60c-src and pp62c-yes, HamT was associated with the tyrosine kinase p59fyn. This association with p59fyn, a potentially important tyrosine kinase in lymphocytes, might explain HaPV's ability to cause lymphoid tumors.