分子生物学第十一章 riboswitch.pptVIP

… an ‘expression platform’ for gene regulation. A metabolite-binding ‘aptamer’ domain and … Riboswitch Functions U U U U U X 3 4 2 1 Direct (protein-free) binding of metabolite to RNA Metabolite-dependent regulation of genes These two activities are accomplished by two functionally separate domains on the RNA: Because of the modular nature of RNA structures, different types of expression platform can be linked to the conserved aptamer domain. This leads to variations in riboswitch mechanism … * Riboswitch Mechanisms This movie showed the most common case for bacterial riboswitches: Ligand binding leads to transcription termination and reduced gene expression. U U U U U X 5′ ORF X * Riboswitch Mechanisms Riboswitches also regulate translation and anti-termination … Ligand binding leads to transcription termination and reduced gene expression. U U U U U X 5′ ORF Ligand binding sequesters the Shine-Dalgarno sequence and reduces gene expression. Ligand binding leads to antiterminator formation and increased gene expression. U U U U U X 5′ A U G ORF X X X 5′ A U G ORF AGGAGG X * Riboswitch Mechanisms They also affect RNA integrity, and perhaps splicing and stability. Ligand binding leads to mRNA cleavage by a new natural ribozyme. X 5′ Ligand binding could control splicing in eukayotes. Possibly, ligand binding to the 3′ untranslated region could affect mRNA stability. A U G ORF X 5′ A U G ORF AG GUACGG A A A A A X 5′ A U G ORF X * Riboswitch Ligands Figure shows the chemical structures of riboswitch ligands and schematics of conserved secondary structure in riboswitches. There are 8 confirmed riboswitches with unique metabolite ligands. Many more conserved RNA motifs are currently under investigation. * Riboswitch Gene Regulation Riboswitches are an important mechanism of gene regulation. For example, nearly 2% of the genes of the model organism Bacillus subtilis appear to be controlled by riboswitches. * Metabolite Recognition tRNA Riboswitch 11-mer TRAP complex Coen