Figure 2. Products of influenza virus replication factor-2 (IREF-2)-dependent unprimed RNA synthesis.
(A) RNase T2 protection assay. Radioactively labeled vRNA products were synthesized in the cell-free viral RNA synthesis system with micrococcal nuclease-treated vRNP (mnRNP) and the v53 model template in the presence of ApG (lanes 1–3), the c53 model template in the presence of ApG (lanes 4–6), and c53 in the presence of the IREF-2 fraction and in the absence of ApG (lanes 7–9). Viral RNA products were hybridized with excess amounts of nonlabeled v53 (lanes 2, 5, and 8) or c53 (lanes 3, 6, and 9), which was followed by digestion with RNase T2. Hybridized and digested RNA samples were extracted, collected, and subjected to 10% Urea-PAGE followed by autoradiography visualization. The closed arrowhead indicates 53-nt-long RNAs. (B) Analysis of the 5'-terminal structure of IREF-2-dependent unprimed vRNA products. [α-32P] GTP-labeled IREF-2-dependent unprimed vRNA products were prepared in the cell-free viral RNA synthesis system. The radioactively labeled 53-nt-long vRNA products were isolated from 10% Urea-PAGE, which was followed by excision and elution from the gel. A portion of the isolated 53-nt-long products was treated with alkaline phosphatase (lanes 2 and 4). Both nontreated and alkaline phosphatase-treated [α-32P] GTP-labeled unprimed vRNA products were digested with RNase T2 (lanes 1–4) or snake venom phosphodiesterase (lane 5). The digested materials were spotted onto a polyethylenimine (PEI)-cellulose thin layer and developed with 1 N acetic acid-4 M LiCl (4:1, v/v) (left panel; lanes 1 and 2) or 1.6 M LiCl (right panel; lanes 3–6) and visualized by autoradiography. For mobility standards, nonradiolabeled AMP, ADP, and ATP were also subjected to thin-layer chromatography and are indicated on the left side of each panel. For a marker of pppAp, [γ-32P] ATP-labeled v53 synthesized using T7 RNA polymerase was also subjected to RNase T2 digestion and then to thin-layer chromatography (lane 6). The expected nucleotide positions are indicated on the right side of each panel by closed arrowheads.