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16 BIO 326R Attenuation March 2

16 BIO 326R Attenuation March 2 - BIO 326R Attenuation...

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BIO 326R Attenuation
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Tryptophan operon review operator promoter Operator and promoter overlap trp E trp D trp D trp B trp A trpR tryptophan trpR tryptophan trpR tryptophan Binding of repressor trpR to operator prevents transcription. By this simple model we would predict that a trpR null mutation (no functional trpR protein) would continuously transcribe this operon at a high rate But that’s not what happens…
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Tryptophan operon: Attenuation  trp E trp D trp D trp B trp A 1 2 3 4 Protein coding sequences - tryptophan synthesis enzymes 5 ORFs on one mRNA rbs Closer look at the transcription unit (Not to scale) Leader attenuator RNA from regions 1,2,3 and 4 have complementary sequences Region 2 is complementary to both regions 1 and 3. Region 3 is complementary to Both regions 2 and 4. +1 Leader peptide ORF
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RNA from regions 1,2,3 and 4 have complementary sequences Region 2 is complementary to both regions 1 and 3. Region 3 is complementary to Both regions 2 and 4. 1 2 3 4 1 2 3 4 1 2 3 4 RNA transcribed from this DNA can form two different secondary structures 3+4 forms a rho- independent terminator 2+3 structure does not terminate – called a “ preemptor Attenuator region UUUU UUUU UUUUNNNN
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Transcription of the attenuator region trp E trp D trp D trp B trp A 1 2 3 4 rbs RNA pol rbs trp E trp D trp D trp B trp A 1 2 3 4 rbs RNA pol rbs 1 Ribosome binds Shine-Delgarno RBS, begins translation
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Translation of the leader peptide during 
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