IGF-II sequences lacking the E-peptide can convert RIE-1 cells to a reovirus-resistant phenotype. Two independent clones of RIE-1 cells transfected with plasmids expressing native (IGF-II) and mutant (IGF-IIA62T) proteins without the carboxyl terminal extension-peptide (E-peptide) were challenged with serial dilutions of reovirus type 1 as described in Figure 4. Native IGF-II protected RIE-1 cells from reovirus infection (IGF-II(a) and IGF-II(b)), while the IGF-IIA62T mutant (IGF-IIA62T(a) and IGF-IIA62T(b) did not. Non-infected RIE-1 cells (C), and infected 6B72, and RIE-1 cells were included as controls. Expression of Igf2 transgenes (lower panel) was monitored by Northern blot hybridization, and the expression of Igf2 in RIE-1 cells is shown for comparison. The native IGF-II (small arrow) is slightly larger than the cDNA constructs (larger arrow), whereas the double-sided arrow marks the constitutively expressed GAPDH, as shown. Expression of Igf2 in 6B72 is not shown.