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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); has effector as well 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 / corresponding binding sites effector = inducer: arabinose Autoregulation of AraC and CAP regulation of the operon Regulation of transcription in Prokaryotes: additional ways/events 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 Os (two and two at a time) DNA looping RNAP prevented from binding to promoter 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 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 activated kinase - autophosphorylation of the transmitter domain (transfers usually g phosphate from ATP to itself) ... View Full Document

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