Non-AUG-Initiated Internal Translation of the L* Protein of Theiler's Virus and Importance of This Protein for Viral Persistence

Abstract

Theiler's virus is a neurotropic murine picornavirus which, depending on the strain, causes either acute encephalitis or persistent demyelinating disease. Persistent strains of Theiler's virus (such as DA) produce an 18-kDa protein called L* from an open reading frame overlapping that encoding the viral polyprotein. Neurovirulent strains (such as GDVII) are thought not to produce the L* protein, as the alternative open reading frame of these strains starts with an ACG codon instead of an AUG codon. However, we observed that both persistent and neurovirulent strain derivatives can produce two forms of the L* protein through unusual type II internal ribosome entry site-mediated translation. A full-length 18-kDa protein can be expressed from an ACG or an AUG initiation codon, whereas an N-terminally truncated 15-kDa product can be translated from a downstream AUG initiation codon. The expression of the 18-kDa form is required for efficient persistence of DA virus derivatives in the central nervous system.

Internal Initiation Stimulates Production of p8 Minicore, a Member of a Newly Discovered Family of Hepatitis C Virus Core Protein Isoforms

“…Like the hypervariable region of the HCV E2 envelope protein (15), products of the Nterminal portion of ARFPs are not required for HCV infection (29). The ARFPs may be analogous to the L* proteins of Theiler's virus (23), which are required for viral persistence but not for viral replication (44). The following three different mechanisms have been reported to mediate expression of HCV's ARF: ribosomal frameshifting (10,54), transcriptional slippage (10,33,54), and internal initiation (5,47).…”

Influence of the Leader protein coding region of foot-and-mouth disease virus on virus replication

“…Typically, such transcriptional errors within the ORF, during RNA replication, will be lethal, but it is also possible that they may enhance the utilization of alternative ORFs, in a different region frame, e.g. for the L* protein of Theiler's murine encephalomyelitis virus (TMEV) (Kong & Roos, 1991;van Eyll & Michiels, 2002) and the alternative ORF (termed 2B*) within the 2B coding region of EMCV (Loughran et al, 2011). It is interesting that this alternative ORF within EMCV occurs just downstream of a conserved GGUUUUU motif and the frameshift mutations identified within the FMDV variants V1 and V3 involved an error within a run of four or five Us (see Fig.…”

Theiler's Virus L* Protein Is Targeted to the Mitochondrial Outer Membrane

“…The L* protein encoded by this virus is the sole protein encoded by an alternative ORF within the picornavirus family (19). L* was found to play an important role in the establishment of persistent CNS infections by TMEV (4,7,25). In vitro, L* facilitates viral infection of macrophages (17,23,24), possibly through antiapoptotic activity (7,9).…”

“…Subcellular localization of the TMEV-encoded L* protein was analyzed in HeLa cells infected for 24 h with 5 PFU per cell of the wild-type TMEV DA1 strain or with the OV90 mutant virus, in which AUG codons 1, 5, and 41 of L* are mutated to ACG and which therefore expresses minimal amounts of L* (25). Cells were processed for indirect immunofluorescence as described previously (18).…”