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

Cleavage of the propeptide region of v-sis is not required for its activity, as demonstrated initially in previous work from this laboratory in which the Lys-Arg cleavage site of v-sis was mutated to Asn-Ser with no change in biological activity (Saner et al., 1986) . In subsequent studies from our lab, the KR to NS mutation has been incorporated into a variety of membrane-anchored derivatives (Hannink and Donoghue, 1986b; Lee and Donoghue, 1992; Xu et al., 1993) , including sis-G and sis-G-ER-, with no effect on biological activity. This is an important point, as the constructs that are retained in the early Golgi, sis-E1 and sis-El-G, would not be expected to undergo this cleavage process. Thus, we can conclude that the inactivity of these proteins is not due to their lack of propeptide cleavage.