12 BIO 326R Transcription

12 BIO 326R Transcription - BIO 326R Transcription What's a...

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BIO 326R Transcription
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What’s a gene?  Transcription Unit Functional unit of heridity Not just protein encoding Untranslated regions Structural and other RNAs Not just the transcribed region Mutations in promoters and other regulatory regions are heritable and can produce different phenotypes
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RNA polymerase Multi subunit enzyme Bacterial RNA polymerase “Core enzyme” is four subunits: 2 alpha, 1 beta, 1 beta’ Sigma subunits provide promoter specificity Must scan DNA and recognize promoter Initial binding of polymerase complex relies on proper recognition of promoter sequence. i.e. it must recognize sequence of promoter with high specificity There are about 4.6 million base pairs in the E. coli genome, containing about 5,000 genes. Promoters only work in one direction, i.e. they are unidirectional Highly processive No primer required to initiate polymerization Needs to stop
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Transcriptional unit Promoter +1 Denotes transcriptional start site +1 is first transcribed base. The base preceding “+1” is “-1.” (There is no zero!) By convention, the RNA produced is used as the reference for the orientation of the gene: The 5’ end of the gene is where the transcription starts, the 3’ end is where transcription ends. Upstream regulatory elements
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Transcription – bacterial promoters  -10 region TATAAT TTGACA -35 region +1 16-18 bp Pribnow box Upstream Downstream 5’ → 3
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Consensus sequence TATAAT T CG AAT TATA T T T C TAAT TATAAT T T T T AT TATAAT TAT TTA CG TAAT T C TA C T TA C AAT 10 different promoter sequences from 10 different genes aligned Consensus sequence – Some bases may be more “conserved” than others Actual compiled consensus: T(80) A(95) t(45) a(60) a(50) T(96)
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The “best” promoter?  Most promoters are not designed for maximal polymerase binding and transcription This allows modulation of expression – allows changes in transcriptional rate either up or down, and makes them easier to turn off and on. The theoretical maximum transcription of a promoter is
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12 BIO 326R Transcription - BIO 326R Transcription What's a...

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