Mechanism of interferon action: functionally distinct RNA-binding and catalytic domains in the interferon-inducible, double-stranded RNA-specific adenosine deaminase.
The 1,226-amino-acid sequence of the interferon-inducible double-stranded RNA-specific adenosine deaminase (dsRAD) contains three copies (RI, RII, and RIII) of the highly conserved subdomain R motif commonly found in double-stranded RNA-binding proteins. We have examined the effects of equivalent site-directed mutations in each of the three R-motif copies of dsRAD on RNA-binding activity and adenosine deaminase enzyme activity. Mutations of the R motifs were analyzed alone as single mutants and in combination with each other. The results suggest that the RIII copy is the most important of the three R motifs for dsRAD activity and that the RII copy is the least important. The RIII mutant lacked detectable enzymatic activity and displayed greatly diminished RNA-binding activity. Site-directed mutations within the highly conserved CHAE sequence of the postulated C-terminal deaminase catalytic domain destroyed enzymatic activity but did not affect RNA-binding activity. These results indicate that the three copies of the RNA-binding R subdomain are likely functionally distinct from each other and also from the catalytic domain of dsRAD.
Liu
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Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara 93106, USA.
Samuel
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D000243:Adenosine Deaminase / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D004279:DNA, Viral; D004790:Enzyme Induction; D018698:Glutamic Acid / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D006801:Humans; D007372:Interferons / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012330:RNA, Double-Stranded / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
D004279:DNA, Viral; D012330:RNA, Double-Stranded; D016601:RNA-Binding Proteins; D018698:Glutamic Acid; D006639:Histidine; D007372:Interferons; C567955:ADARB1 protein, human; D000243:Adenosine Deaminase