FIG. 7.

Substrate specificity of the SARS-CoV nsp13-associated RNA 5′-triphosphatase activity. The substrate RNA, 5′-GGGAAAAA-3′, was synthesized by in vitro transcription in the presence of [α-³²P]GTP (lanes 1 to 4) or [γ-³²P]GTP (lanes 5 to 8). Reactions were performed as described in Materials and Methods. The RNA substrates were incubated without protein (lanes 1 and 5), with MBP-nsp13 (lanes 2 and 6), with MBP-nsp13_KA (lanes 3 and 7), or with alkaline phosphatase from calf intestine (CIP) (lanes 4 and 8). Reaction products were separated by thin-layer chromatography on polyethyleneimine cellulose-F plates and visualized by autoradiography. Reaction mixtures were incubated for 60 min (lanes 2, 3, 6, and 7) or 30 min (lanes 4 and 8).