MBB331_Week11-Fall-2011

Control at level of mrna stability stability of a

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Unformatted text preview: RNA that pairs with ompF mRNA around ompF its Shine-Dalgano ribosome binding site binding Translation is blocked & hybrid Translation blocked susceptible to RNases that cut dsRNA 42 Lewin Genes VII 2000 Oxford University Press (iii) ANTISENSE RNA • Stem-loop in rpoS blocks Shine-Dalgarno • Small RNA (sRNA) complementary to rpoS mRNA frees up ShineDalgarno 43 Eukaryotic gene expression: post­transcriptional control • 1. Control at level of mRNA stability • Stability of a transcript will affect translatability-offers Stability means for control of gene expression means • Prokaryotic transcripts t1/2 ~ 3 min-quick adaptation of gene expression gene • Eukaryotic transcripts: – Short lived transcripts (t1/2 of few minutes), expression required for brief periods - eg. c-Fos & eg c-Fos c-Jun expression induced transiently for S phase onset onset – Long lived transcripts (t1/2 of many hours), continued expression required - eg. β -globin t1/2 of 44 eg -globin 10 hours 10 3´ UTR IREs: TARGETS FOR mRNA DEGRADATION -transferrin transports iron into the cell, responsiveness controlled at level of mRNA stability Weaver 2002 Molecular Biology Ed. 2 • Transferrin receptor mRNA: 3´ UTR IREs form stem-loops.. Transferrin When iron low ---> aconitase binds IRE & inhibits adjacent iron destabilizing sequences ---> mRNA stable mRNA • When iron high ---> aconitase binds iron & aconitase When iron 45 releases from IREs ---> transferrin receptor mRNA unstable transferrin ACONITASE DESTABILIZATION OF TfR mRNA Weaver 2002 Molecular Biology Ed. 2 • Aconitase binds iron, dissociates from transferrin receptor mRNA 3´ UTR IREs…. Unprotected IRE stem-loops susceptible to attack by RNase, which clips mRNA & exposes its 3´-end for degradation its 46 RNA interference (RNAi & siRNA) RNA • • Reduces gene expression by Reduces targeted degradation of specific mRNAs specific an experimental technique an exploiting naturallyexploiting occurring process for RNA occurring degradation degradation siRNA for mammalian postsiRNA transcriptional gene silencing transcriptional requires ~20 nt dsRNAs requires DICER DICER RISC 47 RNA interference (RNAi & siRNA) RNA 48 -an RNA-directed RNA polymerase (RdRP) c...
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