REGULATION OF CYTOSKELETAL ASSOCIATION BY A BASIC-AMINO-ACID MOTIF INPOLYOMA-VIRUS MIDDLE T-ANTIGEN

The subcellular localization of many oncogenic proteins is thought to be important for their function. In the case of the middle T antigen o f the DNA tumour virus, polyoma, localization to membranes in a specif ic manner is essential for its cellular transforming activity. To inve stigate factors that influence this localization, heterologous membran e targetting sequences were substituted for the middle T antigen trans membrane domain and the properties of the resulting proteins studied. Whereas G-terminal lipid modification derived from the H-ras CaaX box restored oncogenic activity to nontransforming truncated middle T anti gen species, N-terminal myristylation from pp60c-src did not. Furtherm ore, a region, rich in basic amino acids and adjacent to the middle T transmembrane domain, was found to mediate association with detergent- insoluble cytoskeleton. Go-operation between the basic motif and neigh bouring membrane binding domains resulted in specific localization of proteins to particular membrane sites, characterized by the associatio n with subcellular structures, likely to be cytoskeletal in nature. Th ese results demonstrate that the cellular localization of MT is regula ted by at least two determinants, a transmembrane sequence which confe rs membrane binding and a basic motif which specifies a particular sit e within the membrane.