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

When looking for sis-E1-G protein on the surface of the same cell, D demonstrates that there is no detectable surface staining. As with Fig. 4 , these were transient expression assays, and the typical percentage of cells expressing the transfected fusion constructs was ,,ol-5 %. We deliberately examined cells expressing high levels of protein within the cell, so that even weak cell surface staining would be detectable. Although deliberate selection of high-expressing cells tended to obscure any detail present in the permeabilized cells, the issue of whether sis-E1 and sis-E1-G are in fact localized to the early Golgi complex is addressed in colocalization experiments in the subsequent section. The cell featured in Fig. 5 is representative of all sis-El-G-expressing cells, in that we were never able to detect protein on the cell surface. Thus, the cis-Golgi retention signal of the E1 glycoprotein, when appended to the v-sis protein, results in efficient retention of the fusion protein to an intracellular compartment.