Analysis of interaction between RNA aptamer and protein using nucleotide analogs.

Non-structural protein 3 (NS3) derived from Hepatitis C virus (HCV) is essential for viral proliferation and has two functional domains; trypsin-like serine protease and helicase. Recently we obtained three types of RNA aptamers (G9-I, -II and -III) bound to NS3 protease domain (delta NS3) by in vitro selection and confirmed their strong inhibition for protease activity. These aptamers have a common sequence, 5'-GA(A/U)UGGGAC-3', forming a loop structure by Mulfold secondary structure modeling. G9-I shows a three-way junction and G9-II and -III have four-way junction structures. To characterize the active structure of these aptamers, we applied modification interference analysis using nucleotide analogs and identified common important nucleotides in these three aptamers.