Lec15+notes

Lec15+notes - Regulation of Gene Expression Expression is...

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1 Regulation of Gene Expression Expression is controlled at many points Operons allow a single control point to control multiple genes Transcription initiation is controlled by repressors and activators Small metabolites act as co-repressors and co-activators or inducers. Translation initiation can also be controlled Frameshifting control Attenuation by ribosomes Control of termination and translation by riboswitches
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2 Gene expression can be controlled at many points Gene numbers (replication, amplification, loss) RNA concentration Protein concentration Transcriptional control RNA turnover protein turnover Translational control Protein modification Active Inactive Transcription rates Translation rates RNA decay rates Protein decay rates
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3 Gene organization in bacteria: Operon structure. In bacteria, often genes with related functions are next to each other in the genome. Expression of the genes is controlled in concert: operon . Transcription from one promoter makes an mRNA with coding regions for all the proteins. This is called a polycistronic mRNA . Control of expression is imposed on the entire set of genes using one or a few regulatory points. A dispersed group of genes (or operons) under common control is called a regulon .
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4 Mechanisms of bacterial transcriptional regulation: Basal expression level and the intrinsic strength of the promoter. New sigma factors activate different (new) sets of promoters. Positive regulation in which an activator protein and/or co-activators are required to bind DNA at an activation site or enhancer and increase transcription. Negative regulation in which a repressor protein and/or co-repressors are required to bind the DNA at an operator to decrease transcription. Ch-ch-ch-changes… Transcriptional activation , during which positive regulation is applied . Induction or derepression , during which negative regulation is relieved . Repression , during which negative regulation is applied . Multiple kinds of regulation can be superimposed on the same promoter.
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5 New sigma factors . Sigma70 and Sigma32 are two distinct sigma factors. Sigma70 is the "standard" sigma factor that directs core RNAP to standard promoters. Sigma32 is the “ heat shock” sigma factor directs RNAP to a special the heat shock promoters. mRNA for sigma32 is always produced but is not well translated. In response to heat shock, sigma32 is induced, probably through melting of a structure in its mRNA that represses translation. Once sigma32 is made, the core RNAP can initiate at the heat shock promoters.
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6 Control of transcription initiation at the Tryptophan operon (encodes enzymes required to make tryptophan). Transcription initiation at the trp promoter is
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Lec15+notes - Regulation of Gene Expression Expression is...

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