Tethered Domains and Flexible Regions in tRNase Z(L), the Long Form of tRNase Z

tRNase Z, a member of the metallo-β-lactamase family, endonucleolytically removes the pre-tRNA 3′ trailer in a step central to tRNA maturation. The short form (tRNase Z(S)) is the only one found in bacteria and archaebacteria and is also present in some eukaryotes. The homologous long form (tRNase Z(L)), exclusively found in eukaryotes, consists of related amino- and carboxy-domains, suggesting that tRNase Z(L) arose from a tandem duplication of tRNase Z(S) followed by interdependent divergence of the domains. X-ray crystallographic structures of tRNase Z(S) reveal a flexible arm (FA) extruded from the body of tRNase Z remote from the active site that binds tRNA far from the scissile bond. No tRNase Z(L) structures have been solved; alternative biophysical studies are therefore needed to illuminate its functional characteristics. Structural analyses of tRNase Z(L) performed by limited proteolysis, two dimensional gel electrophoresis and mass spectrometry establish stability of the amino and carboxy domains and flexibility of the FA and inter-domain tether, with implications for tRNase Z(L) function.