BIOCHEMICAL-STUDIES ON CAPPED RNA PRIMERS IDENTIFY A CLASS OF OLIGONUCLEOTIDE INHIBITORS OF THE INFLUENZA-VIRUS RNA-POLYMERASE

A synthetic 67-nt RNA substrate, containing a P-32-labeled cap-1 struc ture (m(7)G(32)pppGm) was specifically cleaved by the influenza virus RNA polymerase (EC 2.7.7.48) to yield a single capped 11-nt fragment c apable of directly priming transcription. An analysis of systematic tr uncations of this RNA substrate demonstrated that an additional nucleo tide beyond this cleavage site was required for cleavage. The minimal RNA chain length required for priming activity was found to be 9 nt, w hile in contrast an RNA chain length of at least 4 nt was required for efficient binding to the viral polymerase. On the basis of these chai n length requirements we show that a pool of capped oligonucleotides t oo short to prime transcription, but long enough to bind with high aff inity to the viral polymerase, are potent inhibitors of cap-dependent transcription in vitro.