Expression of Theiler's murine encephalomyelitis virus protease 3C and polymerase 3D in Escherichia coli and characterization of monospecific sera

Pathogenesis of Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus belongs to the family of picornaviridae. Picornaviruses are small ( “pico”), phylogenetically related RNA viruses. Based on different biochemical and biophysical characteristics picornaviruses are subdivided into four groups: enteroaphthovirus (foot-and-mouth disease virus), cardiovirus [encephalomyocarditis virus (EMCV), Mengo virus], and rhinovirus (human rhinovirus). Theiler's murine encephalomyelitis virus was originally classified among the picornaviridae as an enterovirus because of its biological similarities with poliovirus. Further comparison of the complete genome of TMEV BeAn 8386 strain identifies remarkable similarities at the level of nucleotides and predicted amino acids between BeAn and the cardioviruses EMCV and Mengo virus. Theiler's murine encephalomyelitis virus is a single-stranded nonenveloped RNA virus. The viral RNA is of positive sense, having the same polarity as mRNA. Viral mRNA lacks the cap structure found at the 5’ end of almost all eukaryotic mRNAs.

Polyprotein processing of Theiler's murine encephalomyelitis virus

To investigate polyprotein processing of Theiler's murine encephalomyelitis viruses, we analyzed in vitro translation reactions programmed by in vitro-derived transcripts from an infectious full-length cDNA clone of the DA strain of Theiler's virus. To help identify the proteinases that carried out the processing, we modified the DA cDNA clone transcription template by linearization with different restriction endonucleases that generate templates of different lengths or by constructing linker insertion or deletion mutations or both in putative proteinase-coding regions. Protein 3C carried out most of the cleavages of the polyprotein, as is true for the other picornaviruses that have been studied. A second proteinase also appeared active at the LP12A-2B junction. A protein of slightly faster mobility than the leader protein was seen with translation of transcripts derived from DA cDNA but not GDVII cDNA. This protein may be synthesized from an alternative initiation site in the DA leader-coding region out of phase with the polyprotein reading frame. Our findings are relevant to ongoing investigations of the abnormal virus expression seen in DA virus late demyelinating disease, since polyprotein processing is critical in regulating picornaviral gene expression.