Section L Regulation of Transcription in Prokaryotes原核生物转录调控区L.pptVIP

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Section L Regulation of Transcription in Prokaryotes原核生物转录调控区L.ppt

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Section L Regulation of Transcription in Prokaryotes原核生物转录调控区L

Section L: Regulation of transcrip. in Prok. Yang Xu, College of Life Sciences Section L: Regulation of transcrip. in Prok. Yang Xu, College of Life Sciences Attenuation Reason of attenuation: Attenuation effect depends on the fact that transcription and translation are tightly coupled in E. coli; translation can occur as an mRNA is being transcribed. Sequence 1: ? The 3’OH-end of the trp leader peptide coding sequence overlaps complementary sequence 1; ? the two trp codons are within sequence 1. Stop codon: The stop codon in the leader sequence is between sequence 1 and sequence 2. 3:4 hairpin: It is a conditional terminator (attenuator). When the tryptophan is non-starved, the 3:4 hairpin forms in the mRNA. Coordination: As transcription of the trp operon proceeds, the RNA polymerase pauses at the end of sequence 2 until a ribosome begins to translate the leader peptide. Section L: Regulation of transcrip. in Prok. Yang Xu, College of Life Sciences Importance of attenuation 700-fold regulatory effect: Attenuation: The presence of tryptophan gives rise to a 10-fold repression of trp operon transcription through the process of attenuation alone. Trp repressor: Combined with control by the trp repressor (70-fold), this means that tryptophan levels exert a 700-fold regulatory effect on expression from the trp operon. His operon: For example Histidine codons: The His operon has a leader sequence which encodes a peptide with seven successive histidine codons. Only mechanism: The His operon has no repressor-operator regulation, and attenuation forms the only mechanism of feedback control. Other operons: Attenuation occurs in at least six operons that encode enzymes concerned with amino acid bio-synthesis. Section L: Regulation of transcrip. in Prok. Yang Xu, College of Life Sciences L3 Trans. regulation by alternative s factor Sigma factor Heat shock Bateriophage s factor hsp47 groel Section L: Regulation of transcrip. in Prok. Yang Xu, College of Life Science