Construction of a recombinant cDNA of echovirus 6 that established a persistent in vitro infection.

cDNA clones of lytic acute and nonlytic persistent strains of echovirus 6 were used to construct a recombinant cDNA. The 3' region of the infectious wild-type cDNA genome, which extended from VPg to the end of the noncoding region, was exchanged with the cDNA fragment representing the same region of the persistent viral genome. Sequence analyses indicated that there was one mutation in the 3C protease and eight mutations in the 3D polymerase. Transfection of the recombinant cDNA into WISH cells resulted in cellular survival and synthesis of viral RNA. The viral RNA was retained in the transfected cell line after cultivation for 7 months. Supernates, collected from cell cultures at 1, 3, and 7 months after transfection with the recombinant cDNA, transmitted the viral RNA to uninfected cells. The results indicated that the recombinant cDNA established a persistent echovirus 6 infection that was transmissible by nonlytic virus particles.