8 DNA Technology - Chapter10 Posttranscriptional...

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Chapter 10 Recombinant DNA Technology
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Posttranscriptional Regulation - Review ********* mRNA Degradation and Stabilization ************ Specific sequences in an mRNA can cause the stabilization or decay of a particular mRNA by either preventing access to nuclease or recruiting nucleases. Example of a stable mRNA: Globin RNase AUG UAA AAAAAAAAA Stabilization
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Posttranscriptional Regulation mRNA Degradation and Stabilization Specific sequences in an mRNA can cause the stabilization or decay of a particular mRNA by either preventing access to nuclease or recruiting nucleases. RNase AUG UAA AAAAAA Promotion of decay Example of unstable mRNA: growth-promoting genes What would happen if a cell grows uncontrollably ????
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Cells Have A Surveillance Mechanism To Detect And Degrade mRNA Containing Premature Stop Codons Nonsense-Mediated Decay
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Transport of an mRNA to the cytoplasm Usually only fully processed mRNA can be exported out of the nucleus Posttranscriptional Regulation
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HIV bypasses the normal restriction for the transport of unspliced RNA Transport of an mRNA to the cytoplasm Usually only fully processed mRNA can be exported out of the nucleus -HIV virus has devised a way to override this process with the Rev RNA-binding protein to produce critical viral proteins.
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Cells Have A Surveillance Mechanism To Detect And Degrade mRNA Containing Premature Stop Codons Nonsense-Mediated Decay
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Mammalian Cell Pre-mRNA 5'-End Quality Control Pre-mRNA DXO DXO GpppN ppp p GpppN OH PPi p CTD Pol II Pol II P 5 P 5 P 5 C.E. P 5 P 5 P 5 P 5 P 2 P 2 P 2 P 2 P 5 P 5 P 5 P 5 mRNA eIF4E m 7 Gppp AAAAAn mRNA Decay mRNA Translation Nuclear C y t op la s m ic m Gppp 7 AAAAAn CBP m Gppp 7 Pol II m Gppp 7 Splicing Pre-mRNA 5' End Quality Note: Incorrectly capped pre-mRNAs are not further processed
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Posttransctiptional Regulation Translational Control Proteins that bind to the mRNA can inhibit translation AUG UAA AAAAAA Protein AUG UAA AAAAAA No Protein Translation is on Translation is off
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siRNA are short interfering RNA sequences that are perfectly complementary to the target mRNA and triggers cleavage of the mRNA target. miRNA involves short RNA sequences that are not perfectly complementary to the target mRNA and result in the translational silencing and/or decay of the mRNA. Two classes of small noncoding RNAs can silence gene expression: microRNAs ( miRNA ) and small interfering RNAs ( siRNA ) RNA Silencing by Small Noncoding RNAs Utilize short 21-23 nucleotide RNAs that can target an mRNA for translational silencing or mRNA decay.
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Both siRNA and miRNA are processed by a similar mechanism The RNA is assembled into a complex referred to as RISC (RNA- Induced Silencing Complex) dsRNA is cleaved into 21-23 nt fragments by Dicer Depending on the complementarity of the short RNA to the target mRNA, it either results in the degradation of the mRNA or translational silencing.
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