Encephalomyocarditis viruses with short poly(C) tracts are more virulent than their mengovirus counterparts

We have constructed three cDNA clones of encephalomyocarditis virus strain R (EMCV-R) with poly(C) tracts of C4, C9, and C20. RNA transcribed from these cDNAs was infectious to HeLa cells, and the resultant viruses grew well in this system, albeit with plaque sizes that were proportional to the poly(C) length. When injected into mice, the progeny viruses were only slightly less pathogenic than EMCV-R, and the observed degree of attenuation was not nearly as dramatic as for equivalent mengoviruses with similar short poly(C)s. Short-tract poly(C)-mediated attenuation is therefore highly dependent on viral genomic context.