Catalytically inactive PUS10 selectively binds only certain other tRNAs. (A) Radiolabeled tRNAs for Trp, Gln, Ala, and Phe (indicated below the panels) were incubated with increasing concentrations of h-PUS10, resolved by native PAGE, and visualized by phosphorimaging. (B) Reactions similar to those in A using i-PUS10 with tRNATrp and tRNAAla. (C) Reactions similar to those in A using h-PUS10 with tRNAiMet and tRNAAU-Ala and their mutants (mut-iMet and mut-AU-Ala) where sequences at positions 59–60 were interchanged as described in the text. (D) Separately radiolabeled tRNATrp (*Trp) along with increasing concentrations of unlabeled tRNAs (indicated above the panels) for Trp, Gln, initiator Met, and Phe were incubated with h-PUS (20 µM), resolved by native PAGE, and visualized by phosphorimaging. The first lane in each panel contains only the radiolabeled tRNATrp, with no unlabeled tRNA or h-PUS10. (E) Reactions similar to A after separate incubations of tRNATrp with nh-PUS10 and ch-PUS10.