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IUB BIOL-L 211 - Transcriptional Regulation in Prokaryotes II

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BIOL-L211 Lecture 19 Outline of Last Lecture I. Alternative Sigma FactorsII. Fla/che Operon Outline of Current Lecture I. DNA Binding ProteinsII. The lac operon of E. ColiIII. Quorum SensingCurrent LectureTranscriptional Regulation in Prokaryotes III. DNA Binding Proteins (ex: lac operon)A. Without Activators/Repressors: RNAP binds weakly to promoters and initiates low transcription levelsB. Activator:1. Binds in front of promoter2. Has DNA binding region and region that interacts with RNAP3. Helps RNAP bind more strongly to promoter4. Yields high levels of gene transcriptionC. Repressor:1. Binds to an operator sequence within the promoter2. Prevents RNAP from accessing promoterThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.3. Inhibits transcription of gene(s)II. The lac Operon of E. ColiA. The lac operon breaks down lactose into glucose (food for the cell), and is regulated by activators and repressors1. Activator: CAP: catabolite activator proteina. Activates transcription when lactose is present2. Without activator, very low levels of transcription3. lac operon has a weak promoter4. Repressor: physically prevents binding of RNAP thus preventing transcription in the absence of lactoseB. lac operon has three genes under the control of a specific promoter1. lacZ: also known as β-galactosidase; cleaves lactose into its components: galactose and glucose2. lacY: transports lactose into cell3. lacAIII. Quorum SensingA. Quorum is not only a biological term, yet it is used to define a phenotype in bacteriaB. At a certain concentration, bacteria can quorum sense (i.e. sense their population density)C. They can then respond to that by changing their gene expressionD. LuxI synthesizes autoinducer1. Autoinducer released into enviroment by cell; can be registered by other cells*note: autoinducer is a molecule, not a protein2. Can trigger activation of activators in other cellsE. LuxR- activator1. Requires high concentration of autoinducer2. Autoinducer binds to LuxR, which then binds to DNA and activates transcription3. Autoinducer accumulation and cell density are proportional4. Autoinducer reaches a threshold that then activates gene expressionF. Unique species of bacteria have unique autoinducers (i.e. cells can only communicate by quorum sensing within their own species)G. Examples:1. Bioluminescencea. LuxR activates transcription of bioluminescence genes when autoinducer is presentb. Vibrio fischeri: bioluminescent bacteriumi. Luciferase expression regulated by quorum sensingii. Luciferase: enzyme that emits lightiii. These bacteria live in the squid Euprymna scolopesiv. Helps squid avoid making a shadow at


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