FIGURE 4.

Boundaries of a gyspy genetic element harboring an IRES activity. (A) Schematic representation of deletions introduced in the 5′ UTR. The numbering is with respect to the 5′ cap site. Segments corresponding to 5′ (B) and 3′ (C) deletions of the 5′ UTR were inserted in between the two cistrons of the bicistronic RNA described in Figure 2B ▶. The resulting uncapped bicistronic RNAs were translated in the RRL (10 μL) at the concentrations indicated. Control assay with uncapped bicistronic RNA containing the entire 5′ UTR was set in parallel (B, lanes 1,2; C, lanes 3,4). At the end of a 60-min incubation, 1μL sample of each assay was analyzed on a 15% SDS-PAGE and subjected to autoradiography. Positions of the molecular weight markers (kD), neomycin (Neo), and β-Gal translation products are indicated.