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) –
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