MBB 331 Lecture 12

What genes make up the ara operon

araB, araA, and araD

What protein regulates the ara operon

AraC

What sugar regulates the ara operon

Arabinose

What is the promoter for the ara operon structural genes

PBAD

What is the promoter for araC

PC

What DNA sites does AraC bind

araI sites and araO sites

The ara operon allows cells to use

arabinose

The entire ara operon revolves around

whether arabinose is present

What does AraC do when arabinose is absent

AraC binds distant sites and forms a DNA loop

What is the result of DNA looping when arabinose is absent

Transcription is repressed

What happens when arabinose binds AraC

AraC changes conformation

What happens to the DNA loop when arabinose is present

The loop breaks

Where does AraC bind after arabinose binds

Adjacent araI sites

What is the result of arabinose binding araC

RNA polymerase is recruited and transcription occurs

What additional protein stimulates ara expression

CAP-cAMP

When is cAMP high

Low glucose

No Arabinose

AraC binds O2 and I1

↓

DNA loop forms

↓

RNAP blocked

↓

Operon OFF

Arabinose Present

Arabinose binds AraC

↓

AraC changes shape

↓

Loop breaks

↓

AraC binds I1 and I2

↓

RNAP recruited

↓

Operon ON

Low Glucose

CAP-cAMP helps recruit RNAP

↓

HIGH transcription

What sugar is metabolized by the gal operon

Galactose

What genes are found in the gal operon

galE, galT, and galK

What regulatory protein activates the gal operon

CRP-CAP

What repressor regulates the gal operon

GalR

What does GalR do

Represses transcription

How does GalR repress transcription

Forms a DNA loop

What protein helps activate gal transcription

CAP-cAMP.

When is activation strongest

Low glucose

What amino acid does the trp operon synthesize

Tryptophan

What genes make up the trp operon

trpE, trpD, trpC, trpB, trpA

What regulatory protein controls the trp operon

Trp repressor (TrpR)

What important sequence is located before the trp operon structural genes

The leader region (trpL)

What mechanism occurs in the leader region

Attenuation

What happens to TrpR when tryptophan is absent

It cannot bind DNA

What happens to transcription when tryptophan is absent

Operon is ON

What acts as the corepressor when there's high tryptophan

Tryptophan

What happens when tryptophan binds TrpR

TrpR can bind the operator.

What is the result when tryptophan is present

Transcription is repressed.

Memory Trick Lac

Sugar turns genes ON

Memory Trick TRP

Product turns genes OFF

What is attenuation

Premature termination of transcription

What determines whether attenuation occurs

Ribosome movement through the leader peptide

What happens when tryptophan is abundant

Ribosome moves quickly and terminator forms

What happens when tryptophan is scarce

Ribosome stalls and anti-terminator forms

What are the two possible lifestyles of lambda phage

Lytic and lysogenic

What major regulatory proteins determine the outcome

cI repressor and Cro

What promoter activates cI during lysogen

PRE

What promoter maintains cI expression

PRM

What protein activates PRE

cII

What is produced from PRE

λ repressor (cI)

What does cI repress

PR and PL

What enzyme is needed to insert lambda DNA into the chromosome

Integrase

What protein promotes lysis

Cro

Which operator does Cro prefer

OR3 first

What happens when Cro binds OR3

PRM is blocked

What is the consequence of blocking PRM

No cI repressor is produced

What protein acts as the key decision-maker

cII

What protein stabilizes cII

cIII

What degrades cII

Host proteases (FtsH)

What happens at low MOI

Low cII → lytic growth

What happens at high MOI

High cII → lysogeny

What cellular event can trigger induction of lytic growth

DNA damage

What bacterial protein becomes activated during the SOS response

RecA

What does activated RecA do

Cleaves λ repressor

What happens when cI is destroyed

Cro is transcribed and lytic growth begins