Deletion or substitution of the aphthovirus 3' NCR abrogates infectivity and virus replication.

The 3' noncoding region (NCR) of the genomic picornaviral RNA is believed to contain major cis-acting signals required for negative-strand RNA synthesis. The 3' NCR of foot-and-mouth disease virus (FMDV) was studied in the context of a full-length infectious clone in which the genetic element was deleted or exchanged for the equivalent region of a distantly related swine picornavirus, swine vesicular disease virus (SVDV). Deletion of the 3' NCR, while maintaining the intact poly(A) tail as well as its replacement for the SVDV counterpart, abrogated virus replication in susceptible cells as determined by infectivity and Northern blot assays. Nevertheless, the presence of the SVDV sequence allowed the synthesis of low amounts of chimeric viral RNA at extended times post-transfection as compared to RNAs harbouring the 3' NCR deletion. The failure to recover viable viruses or revertants after several passages on susceptible cells suggests that the presence of specific sequences contained within the FMDV 3' NCR is essential to complete a full replication cycle and that FMDV and SVDV 3' NCRs are not functionally interchangeable.