RESUMO
The central dogma treats the ribosome as a molecular machine that reads one mRNA codon at a time as it adds each amino acid to its growing peptide chain. However, this and previous studies suggest that ribosomes actually perceive pairs of adjacent codons as they take three-nucleotide steps along the mRNA. We examined GNN codons, which we find are surprisingly overrepresented in eukaryote protein-coding open reading frames (ORFs), especially immediately after NNU codons. Ribosome profiling experiments in yeast revealed that ribosomes with NNU at their aminoacyl (A) site have particularly elevated densities when NNU is immediately followed (3') by a GNN codon, indicating slower mRNA threading of the NNU codon from the ribosome's A to peptidyl (P) sites. Moreover, if the assessment was limited to ribosomes that have only recently arrived at the next codon, by examining 21-nucleotide ribosome footprints (21-nt RFPs), elevated densities were observed for multiple codon classes when followed by GNN. This striking translation slowdown at adjacent 5'-NNN GNN codon pairs is likely mediated, in part, by the ribosome's CAR surface, which acts as an extension of the A-site tRNA anticodon during ribosome translocation and interacts through hydrogen bonding and pi stacking with the GNN codon. The functional consequences of 5'-NNN GNN codon adjacency are expected to influence the evolution of protein coding sequences.
Assuntos
Códon , Fases de Leitura Aberta , Biossíntese de Proteínas , RNA Mensageiro , Ribossomos , Códon/genética , Ribossomos/metabolismo , Ribossomos/genética , Fases de Leitura Aberta/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA de Transferência/genética , RNA de Transferência/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Anticódon/genéticaRESUMO
BACKGROUND: Gastric tube necrosis is a major cause of anastomotic leak after esophagectomy. A correlation has been shown between reduced flux at the anastomotic end of the gastric tube and anastomotic leaks. METHODS: We prospectively studied the effect of intraoperative thoracic epidural bupivacaine and subsequent adrenaline infusion on hemodynamics and flux in the gastric tube. RESULTS: Administering the epidural bolus significantly decreased flux at the anastomotic end of the gastric tube (P < 0.01). Gastric flux was returned to baseline by an adrenaline infusion. CONCLUSIONS: The administration of a thoracic epidural bolus may decrease flux at the anastomotic end of the gastric tube.
