Vaccinia virus E3L interferon resistance protein inhibits the interferon-induced adenosine deaminase A-to-I editing activity

The RNA-specific adenosine deaminase (ADAR1) is an interferon-inducible edi ting enzyme that converts adenosine to inosine. ADAR1 contains three distin ct domains: a N-terminal Z-DNA binding domain that includes two Z-DNA bindi ng motifs; a central double-stranded RNA binding domain that includes three dsRNA binding motifs (dsRBM); and a C-terminal catalytic domain responsibl e for A-to-l enzymatic activity. The E3L protein of vaccinia virus mediates interferon resistance. E3L, similar to ADAR1, also contains Z-DNA binding and dsRNA binding motifs. To assess the possible role of E3L in modulating RNA editing by ADAR1, we examined the effect of E3L on ADAR1 deaminase acti vity, Wild-type E3L protein was a potent inhibitor of ADAR1 deaminase enzym atic activity. Analysis of mutant E3L proteins indicated that the carboxy-p roximal dsRBM of E3L was essential for antagonism of ADAR1. Surprisingly, d isruption of the Z-DNA binding domain of E3L by double substitutions of two highly conserved residues also abolished its antagonistic activity, wherea s deletion of the entire Z domain had little effect on the inhibition. With natural neurotransmitter pre-mRNA substrates, E3L weakly inhibited the sit e-selective editing activity by ADAR1 at the R/G site of the glutamate rece ptor B subunit (GluR-B) pre-mRNA and the A site of serotonin 2C receptor (5 -HT2CR) pre-mRNA; editing of the intronic hotspot (+)60 site of GluR-B was not affected by E3L These results demonstrate that the A-to-l RNA editing a ctivity of the IFN-inducible adenosine deaminase is impaired by the product of the vaccinia virus E3L interferon resistance gene. (C) 2001 Academic Pr ess.