分子生物学英文版教学课件：Ch 14 Translation.pptVIP

* * Topic 8: translation dependent regulation of mRNA and protein stability Here regulation refers cellular processes that deal with defective mRNA and their translated product. * * 8-1: The SsrA RNA rescues (拯救) ribosomes that translate broken mRNAs lacking a stop codon (prokaryotes) The ribosomes are trapped or stalled on the broken mRNA lacking a stop codon The stalled ribosomes are rescued by the action of a chimeric RNA molecule that is part tRNA and part mRNA, called tmRNA. SsrA is a 457-nt tmRNA * * Fig 14-39 SsrA rescues the stalled ribosomes * * 8-2: Eukaryotic cells degrade mRNAs that are incomplete or have premature stop codons. Translation is tightly linked to the process of mRNA decay in eukaryotic cells * * When an mRNA contains a premature stop codon (nonsense codon), the mRNA is rapidly degraded by nonsense mediated mRNA decay. Pre-releasing the ribosome at the nonsense codon prior to reaching the exon-junction complex initiates a talk between the complex and ribosome to remove the 5’ cap from the mRNA Nonsense mediated mRNA decay * * 1. Translation of a normal eukaryotic mRNA displace all the exon junction complex Fig 14-40a * * 2. Nonsense mediated mRNA decay Fig 14-40b * * Non-stop mediated mRNA decay rescues ribosomes that translate mRNAs lacking a stop codon. The lack of a stop codon results in ribosome translation into the poly-A tail to produce poly-Lys at the C-terminus of the polypeptide; the poly-Lys marks the newly synthesized for rapid degradation. Nonstop mediated decay * * Fig 14-40c The ribosome eventually stalls at the 3’ end of the mRNA, which is bound by the Ski7 protein that triggers the ribosome dissociation and recruits a 3’-5’ exonuclease activity to degrade the “nonstop” mRNA. * * The main challenge of translation The structure and function of four components of the translation machinery. (重点) Translation initiation, elongation and termination (具体过程和翻译因子的作用-注意起始阶段原核与真核的不同，重点) Translation-dependent regulation of the s