L* protein of Theiler's murine encephalomyelitis virus is required for virus growth in a murine macrophage-like cell line

We sought to confirm the importance of L* protein for growth of Theiler's m urine encephalomyelitis virus (TMEV) in a macrophage-like fell line, J774-1 . The protein is out of frame,with the polyprotein and synthesized in DA. b ut not GDVII subgroup strains of TMEV. A recombinant virus, DANCL*/GD, whic h substitutes the DA 5' noncoding and L* coding regions for the correspondi ng regions of GDVII and synthesizes L* protein, grew with little restrictio n in J774-1 cells. In contrast, another recombinant virus, DANCL*-1/GD, whi ch has an ACG rather than an AUG as the starting codon of L* protein at nuc leotide 1079, resulting in no synthesis of L* protein, did not grow well. N o significant difference between the rates of adsorption to J774-1 cells of these viruses was observed. RNase protection assay demonstrated that DANCL */GD viral RNA significantly increased, whereas only a minimal increase was observed for DANCL*-1/GD. The present study suggests that L* protein is re quired for virus growth in macrophages.