A glyS T-box riboswitch with species-specific structural features responding to both proteinogenic and nonproteinogenic tRNAGly isoacceptors.
In Staphylococcus aureus, a T-box riboswitch exists upstream of the glyS gene to regulate transcription of the sole glycyl-tRNA synthetase, which aminoacylates five tRNA(Gly) isoacceptors bearing GCC or UCC anticodons. Subsequently, the glycylated tRNAs serve as substrates for decoding glycine codons during translation, and also as glycine donors for exoribosomal synthesis of pentaglycine peptides during cell wall formation. Probing of the predicted T-box structure revealed a long stem I, lacking features previously described for similar T-boxes. Moreover, the antiterminator stem includes a 42-nt long intervening sequence, which is staphylococci-specific. Finally, the terminator conformation adopts a rigid two-stem structure, where the intervening sequence forms the first stem followed by the second stem, which includes the more conserved residues. Interestingly, all five tRNA(Gly) isoacceptors interact with S. aureus glyS T-box with different binding affinities and they all induce transcription readthrough at different levels. The ability of both GCC and UCC anticodons to interact with the specifier loop indicates ambiguity during the specifier triplet reading, similar to the unconventional reading of glycine codons during protein synthesis. The S. aureus glyS T-box structure is consistent with the recent crystallographic and NMR studies, despite apparent differences, and highlights the phylogenetic variability of T-boxes when studied in a genome-dependent context. Our data suggest that the S. aureus glyS T-box exhibits differential tRNA selectivity, which possibly contributes toward the regulation and synchronization of ribosomal and exoribosomal peptide synthesis, two essential but metabolically unrelated pathways.
Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece.
Maria
M
Apostolidi
Unité Mixte de Recherche 7156 Génétique Moléculaire, Génomique, Microbiologie, CNRS, Université de Strasbourg, F-67084 Strasbourg, France.
Nizar Y
NY
Saad
Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece.
Denis
D
Drainas
Department of Microbiology, School of Medicine, University of Athens, 11527 Athens, Greece.
Spyros
S
Pournaras
Unité Mixte de Recherche 7156 Génétique Moléculaire, Génomique, Microbiologie, CNRS, Université de Strasbourg, F-67084 Strasbourg, France.
Hubert D
HD
Becker
Department of Biochemistry, School of Medicine, University of Patras, 26504 Patras, Greece.
Constantinos
C
Stathopoulos
D001483:Base Sequence; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011506:Proteins / Q000378:metabolism*; D012353:RNA, Transfer, Gly / Q000737:chemistry / Q000378:metabolism*; D058928:Riboswitch; D012689:Sequence Homology, Nucleic Acid; D013211:Staphylococcus aureus / Q000235:genetics; D014158:Transcription, Genetic
D011506:Proteins; D012353:RNA, Transfer, Gly; D058928:Riboswitch
Staphylococcus aureus; T-box riboswitch; glycyl-tRNA synthetase; tRNA; transcription regulation