LAC
Operon*
is an INDUCIBLE
operon (i.e.,exhibits negative
control). it is always off and is turned on by an inducer molecule (allolactose) |
CATABOLIC REPRESSION... as long as glucose is present LAC operon is OFF, even if allolactose is present glucose prevents the action of the LAC operon through another regulator-like protein, the Catabolite Activator Protein or CAP and DNA binding site - CAP gene* |
CAP is an allosteric protein, regulated by cAMP |
when
glucose is low - all the ATP
is hydrolyzed favoring high cAMP amounts cAMP-CAP conformation binds to CAP DNA region - favors rapid transcription* when glucose is high - lots of ATP & little cAMP CAP-alone conformation doesn't bind to CAP DNA region - favors slow transcription |
TRP Operon* - a REPRESSIBLE operon... always on & turned off by end product - tryptophan turns off operon by attenuating transcription |
DNA
recognition is via Repressor Proteins &
DNA-Binding Protein Motifs interaction of inducer & repressor & structure of repressor protein helix-turn-helix & binding to DNA, back |