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Spring 09 lecture 19

Spring 09 lecture 19 - Basic review Lactose operon...

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Basic review: Lactose operon : Catabolic Negative regulation Regulatory protein is repressor ; effector = inducer: allolactose (converted lactose) Existence of catabolite activator protein (CAP) Tryptophane operon: Anabolic Negative regulation Regulatory protein is aporepressor ; effector = co-repressor: tryptophan Autoregulation L-arabinose operon Catabolic Positive and negative regulation Same regulatory protein acts as both activator and repressor (regulator) – two different conformations and binding sites effector = inducer: arabinose Autoregulation of AraC and CAP regulation of the operon
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Operator regions – more complicated then previously shown Lac -operon region contains 3 operators: Strongest – commonly shown O1 Downstream O2 – inside lacZ reading frame Upstream O3 All three present – transcription suppressed 1000-fold If either O2 or O3 are missing – 500-fold Both O2 and O3 missing – 20-fold Regulation of transcription in Prokaryotes (cont.) – Multiple operators – auxiliary operators Also: presence of auxiliary operators (O2 and O3) near the functional operator (O1) increases the local concentration of the repressor , so that it can occupy the functional operator (O1) Repressor binds as a tetramer – could bind to all three of them – DNA looping – RNAP prevented from binding to promoter
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Two component regulatory systems Regulation of transcription in Prokaryotes (cont.) – 1. One protein is the sensor-transmitter protein - monitors specific changes in the environment (level of nutrients, pH, solvent concentration-osmolarity etc.); kinase 2. Second protein is response regulator protein - either stimulates or represses regulation of specific genes – changes in gene expression necessary for bacterium to adapt to environmental change
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Two component regulatory system (cont.) Sensor-transmitter usually spans across the cell membrane : sensor is an outer part which detects specific changes in environment transmitter is an inner part which usually acts as a kinase changes in the environment – sensed by sensor ° change of the conformation of sensor domain change of the conformation of sensor domain activates ( change of the conformation) transmitter’s kinase part in the cell
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