ALTERNATIVE TRANSLATION INITIATION SITE IN THE DA STRAIN OF THEILERS MURINE ENCEPHALOMYELITIS VIRUS

Polyprotein processing studies of Theiler's murine encephalomyelitis virus (TMEV), a group of mouse picornaviruses, demonstrated synthesis of a protein we have called 1 during in vitro translations from the RNA of DA, a demyelinating strain of TMEV, but not GDVII, an acute neurovirulent strain. We have proposed that 1 is synthesized from an alternative initiation site in the DA leader (L) coding area out of phase with the polyprotein reading frame (R. P. Roos, W. P. Kong, B. L. Semler. J. Virol. 63:5344-5353, 1989). We now provide support for this proposal from experiments involving in vitro translation of three separate mutations of an infectious DA cDNA clone: DA "1"-1, which contains a base mismatch at the putative initiation codon of 1, DAL-1, which contains a base mismatch at the presumed authentic initiation site of L at the beginning of the polyprotein; and DAL:NheI, which contains nucleotides coding for a four-amino-acid insertion in the L coding area with a termination codon in the 1 reading frame. Our results demonstrate that the DA strain uses an alternative initiation site and reading frame to in vitro synthesize 1. 1 may have a role in the biological activity of the virus.