Subcellular localization of polyoma mT was determined by immuno-fluorescence microscopy, using primary monoclonal/ polyclonal antibodies and secondary polyclonal antibodies conjugated with fluorescent dyes. Our results confirm and extend previous studies reporting the association of mT with an intracellular compartment. However, it is shown that the perinuclear compartment containing the bulk of mT expressed in MRC5 cells is both Brefeldin A resistant and distinct from the known compartments of the secretory pathway. The integrity of most subcellular compartments was not altered by mT expression. However, secondary lysosomes and late endosomes were reorganized in cells expressing mT. Early in cell transformation mT alters several members of the cytoskeletal array, with the most profound effects on actin. In cells coinfected with viruses encoding either mT or pp60csrc, the areas of subcellular localization of both proteins are largely overlapping. In addition, mT recruits She to this subcellular localization indicating that mitogenesis as well as morphological cell transformation may be regulated from this novel intracellular compartment. / Thesis / Master of Science (MS)