title: The CCA-adding enzyme: A central scrutinizer in tRNA quality control.
abstract: tRNA nucleotidyltransferase adds the invariant CCA-terminus to the tRNA 3'-end, a central step in tRNA maturation. This CCA-adding enzyme is a specialized RNA polymerase that synthesizes the CCA sequence at high fidelity in all kingdoms of life. Recently, an additional function of this enzyme was identified, where it generates a specific degradation tag on structurally unstable tRNAs. This tag consists of an additional repeat of the CCA triplet, leading to a 3'-terminal CCACCA sequence. In order to explain how the enzyme catalyzes this extended polymerization reaction, Kuhn et al. solved a series of co-crystal structures of the CCA-adding enzyme from Archaeoglobus fulgidus in complex with different tRNA substrates. They show that the enzyme forces a bound unstable tRNA to refold the acceptor stem for a second round of CCA-addition, while stable transcripts are robust enough to resist this isomerization. In this review, we discuss how the CCA-adding enzyme uses a simple yet very elegant way to scrutinize its substrates for sufficient structural stability and, consequently, functionality.
authors.affiliation: Institute for Biochemistry, University of Leipzig, Leipzig, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Betat
authors.affiliation: Institute for Biochemistry, University of Leipzig, Leipzig, Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Mörl
mesh_terms: D000818:Animals; D001483:Base Sequence; D006801:Humans; D007700:Kinetics; D009690:Nucleic Acid Conformation; D012316:RNA Nucleotidyltransferases / Q000378:metabolism*; D020871:RNA Stability; D012343:RNA, Transfer / Q000737:chemistry / Q000378:metabolism*
chemical_list: D012343:RNA, Transfer; D012316:RNA Nucleotidyltransferases; C023198:tRNA nucleotidyltransferase
keywords: CCA-adding enzyme; RNA decay; tRNA quality control; tRNA surveillance; unstable tRNA