Evidence for dissimilar properties of comoviral and picornaviral RNA polymerases

The poliovirus RNA polymerase has been synthesized in Spodoptera frugiperda cells by using the baculovirus expression system. Crude sonicates of these cells exhibited an RNA-elongating activity of a synthetic oligo(U) primer with poly(A) or cowpea mosaic virus (CPMV) RNA as a template. A similar polymerase activity was found in extracts of insect cells in which foot-and-mouth disease virus (FMDV) proteins, including the putative polymerase, were produced. The analogous CPMV 87K protein and several of its precursors, synthesized in S. frugiperda cells, did not show any detectable polymerase activity in the same assay under a variety of conditions. The results indicate that, in contrast to the picornaviral polymerases, the CPMV polymerase is unable to function in an oligo(U)-primed polymerase assay.