RESUMO
tmRNA is a small, stable prokaryotic RNA. It rescues ribosomes that have become stalled during the translation of mRNA fragments lacking stop codons, or during periods of tRNA scarcity. It derives its name from the presence of two separate domains, one that functions as a tRNA, and another that serves as an mRNA. We have carried out modeling and transient electric birefringence studies to determine the angle between the acceptor stem and anticodon stem of the tRNA domain of Eschericia coli tmRNA. The results of the modeling studies yielded an interstem angle of 110 degrees, in agreement with the lower end of the range of angles (111 degrees -137 degrees ) determined experimentally for various solution conditions. The range of experimental angles is greater than the angles observed for any of the tRNA crystal structures, in line with the presence of a shortened D stem. The secondary structure of the tRNA domain is conserved for all known tmRNA sequences, so we propose that the angle is also conserved. These results also suggest that the region of tmRNA between P2a and P2b may interact with the decoding site of the ribosome.
Assuntos
Escherichia coli/genética , Conformação de Ácido Nucleico , RNA Bacteriano/química , RNA de Transferência/química , Anticódon/genética , Pareamento de Bases , Sequência de Bases , Sítios de Ligação , Birrefringência , Magnésio/farmacologia , Modelos Moleculares , Dados de Sequência Molecular , Ligação Proteica , Estabilidade de RNA , RNA Bacteriano/genética , RNA Bacteriano/metabolismo , RNA Mensageiro/química , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA de Transferência/genética , RNA de Transferência/metabolismo , Ribossomos/química , Ribossomos/genética , Ribossomos/metabolismoRESUMO
Abstract Some evidence and considerations suggest that RNA minihelices based on the acceptor-TΨC stem-loop of tRNAs are the historical, more ancient part of the tRNA structure. These minihelices are substrates for aminoacylation by tRNA synthetases. In the transition from the RNA world to the theatre of proteins, aminoacyl minihelices may have had a role in early systems of peptide synthesis. Such systems would require bringing together aminoacyl groups into close proximity in order for peptide bonds to form. Here we report the design of RNA scaffolds based on pieces of the structure of the P4-P6 domain of the Tetrahymena ribozyme. RNA minihelices were incorporated into these scaffolds and the resulting RNAs could be enzymatically aminoacylated. The RNA scaffolds containing the minihelix-like pieces associated spontaneously to create the presumptive P4-P6 structure and thereby bring together the substrates for aminoacylation. Thus, peptide synthesis with associating RNA scaffolds that contain minihelix-like motifs appears plausible.
