INHIBITION OF INFLUENZA-VIRUS RNA-POLYMERASE BY 5'-CAPPED SHORT RNA FRAGMENTS

We have demonstrated that 5'-capped short RNA fragments inhibit the ex pression of chloramphenicol acetyltransferase (CAT) in the murine 76 c ell line, derived which expresses the genes for the RNA polymerases (P B1, PB2, and PA) and the nucleoprotein (NP) of influenza virus in resp onse to treatment with dexamethasone. We have synthesized 5'-capped sh ort RNA fragments (8-13 ntds long) with a 5'-capped structure (m7GpppG m) using T7 RNA polymerase. The 5'-capped short RNA fragments (8-13 nt ds long) were encapsulated in liposomes and were tested for their inhi bitory effect by a CAT-ELISA assay using the clone 76 cells. The RNA f ragments that were 9-12 ntds long showed inhibitory effects. In partic ular, the 9 ntds long RNA fragment, was highly inhibitory. On the othe r hand, the inhibitory effect of the 13 ntds long RNA fragment was con siderably decreased in comparison with the other short RNA fragments. The minimal RNA chain length required for priming activity was found t o be 12 ntds long, Furthermore, the 5'-capped RNA fragments exhibited higher inhibitory activities than the antisense phosphorothioate oligo nucleotide (PB2-AUG-as, 20 ntds long) complementary to the site of the PB2-AUG: initiation codon. Liposome encapsulation protected the RNA f ragments in serum-containing medium and substantially improved their c ellular accumulation. (C) 1998 Academic Press.