The v-sis oncoprotein loses transforming activity when targeted to the early Golgi complex

In contrast, all of the derivatives that incorporated mutations in the E1 localization signal, including sis-El(Q1), sis-El(Q1)-G, sis-El(ins), and sis-El(ins)-G, exhibited transformation with efficiencies ranging from '~25-50% of sis-G (Table I) . These fusion proteins were consistently less transforming the sis-G, but this phenomenon has been observed before in our lab, with other membrane-anchored derivatives of v-sis (Hannink and Donoghue, 1986a; Lee and Donoghue, 1991; Xu et al., 1993) . This may result from the fact that these membrane-anchored ligands are restricted in their ability to diffuse, and thus less likely to activate receptors as efficiently as the native secreted protein.