Construction of a chimeric Theiler's murine encephalomyelitis virus containing the leader gene of foot-and-mouth disease virus.

The foot-and-mouth disease virus (FMDV) leader coding region (Lb) was cloned into a full-length cDNA of the DA strain of Theiler's murine encephalomyelitis virus (TMEV) replacing the complete L coding region of TMEV. This construct, pDAFSSC1-Lb, was engineered to contain cleavage sites, at the 3' end of the Lb coding region, for both the FMDV Lb and the TMEV 3C proteases. Transcripts derived from this construct were translated in a cell-free system. Analysis of the translation products showed efficient synthesis and processing of TMEV structural and nonstructural proteins as well as a major band that comigrated with FMDV Lb and was reactive with Lb antiserum. A small plaque virus was recovered from BHK-21 cells transfected with RNA derived from pDAFSSC1-Lb. RT-PCR of RNA isolated from DAFSSC1-Lb virus demonstrated a product corresponding in size and sequence to FMDV Lb. DAFSSC1-Lb virus grew slower than parental virus, DAFSSC1, and to a lower titer. The pattern of viral proteins synthesized in DAFSSC1-Lb virus-infected cells was very similar to the pattern in DAFSSC1 virus-infected cells except that significant amounts of FMDV Lb were produced. In addition, extracts from DAFSSC1-Lb-virus-infected cells cleaved an exogenous source of the translation initiation factor, p220, while DAFSSC1-virus-infected extracts did not. Chimeric viruses that contain coding regions from different picornaviral genera may be valuable tools in investigating the function of particular viral proteins and in studying disease pathogenesis.