A metal‐binding motif implicated in RNA recognition by an aminoacyl‐tRNA synthetase and by a retroviral gene product

A randomly generated mutation in Escherichia coli alanine tRNA synthetase compensates for a mutation in its cognate tRNA. The enzyme's mutation occurs next to a Cys‐X₂‐Cys‐X₆‐His‐X₂‐His metal‐binding motif that is distinct from the zinc finger motif found in some DNA‐binding proteins. Instead, the synthe‐tase's metal binding domain resembles the Cys‐X₂‐Cys‐X₄‐His‐X₄‐Cys metal‐binding domain of the gag gene product of retroviruses. For Ala‐tRNA synthetase, the metal bound at the Cys His motif is important specifically for the tRNA‐dependent step of catalysis, and the enzyme‐tRNA interaction is dependent on the geometry of metal co‐ordiNatlon to the enzyme. These data, and the demonstrated sensitivity of RNA packaging to mutations in the metal‐binding domain of the gag gene product of retroviruses, suggest that an aminoacyl‐tRNA synthetase and retroviruses have adopted a related metal‐binding motif for RNA recognition.