Bac gen 4 Positive regulation, attenuation, feedback inhibition

positvely regulated operons are under the control of

activator proteins

genes are transcribed in the presence of an activator when what is bound

the inducer

L-ara operon undergoes _____ regulation

positive

L-ara needs 3 structural genes and a promoter

araA,B,C and Pbad

on the operon, the activator protein ____ binds to a site called ____ in the precense of the inducer ___

AraC, araI, arabinose

upstream of the araI site is where ____ binds

CAP

the AraC protein can ____ and ____

repress and activate

araC needs _____ to activate

arabinose

deletions in araC leads to what in L-ara

superrepressed phenotype where even with arabinose, nothing happens

constitutive mutants and phenotypes

continously produce

if E.coli grew on plates containing D-fucose with L-arabinose as the carbon source, what does this mean

they constitutively express the genes of the ara operon

P1 ara

no inducer, araC is off

P2 ara

inducer- arac is active

araC mutations are not

dominant in complementation tests

the P1 form of AraC is not just inactive, it’s an

anti-activator

how does araC in P1 anti-activate?

bends the dna and binds between operator AraO and araI, which makes it to where it cannot activate transcription

araC mutant can’t do anything in the _____ form, since araC is already bound

P2

how does araC also autoregulate its own expression

without arabinose, araC can bend dna in the region of promoterC

what is another way araC autoregulates its own expressoin

if concentration of araC becomes too high, it binds to the operator araO to prevent transcription from Pc

attenuation of transcription

transcription begins at the promoter but terminates it before rna polymerase reaches structural gene; 2nd layer of control

expression of tnpR is not effected by concentrations of

tryptophan

mutations in tRNA trp _____ expression of the trp operon, which shows

increase, showing that trp operon is sensing the amount of tryptophan cound to tRNA tnp

trna tnp regulation targeted a leader region called

trpL

deletion of tnpL elminates regulation by

attenuation

deletions of tnpL and tnpR cause

constitutive expression

attenuation is based on if ______ form in the leader rna

hairpins

the hairpin that forms in the trp operon is determined by

levels of tRNA trp

if tryptophan is low, trna trp is

low

when the ribosome encounters the trp codon without trnatrp, then it

stalls, unable to insert tryptophan

formation of ____ hairpin causes rna polymerase to terminate transcription

3:4

hairpin 2:3

transcription continues

tnpL mutation causes

no 2:3 hairpin

feedback inhibition is in the ____ operon, common in biosynthetic pathways

trp

feedback inhibition of trp starves the cell for

tryptophan